He could make weapons, as his thing to do next.  He's got acid in very large quantities, and that will let you make large quantities of some relatively weak and tiny things that go boom.

He doesn't want to make weapons.  He doesn't want his knowledge to be used to hurt people.  He doesn't want that to be his meaning to Golarion.

And he's Evil, so what he wants, should be enough of an answer.  That's the whole point of being Keltham instead of a median dath ilani.

Yeah, his brain isn't actually buying that at all.

The people in Nidal - are hurting.

It matters to them a lot more than any of this matters to Keltham.  

Carissa's school instructor got soul-trapped and Keltham has not been asking questions about what happened to him exactly.

And that also matters to Keltham and he cannot, actually, live in denial about that, either, no matter how much it flaming resembles all of the smug, satisfied opinions that people around him politely didn't express, but that he knew they were thinking, about how maybe Keltham would just grow out of it and turn into a median dath ilani one day.

It may not even be the Lawful answer.  He'd be destroying a lot of their value for a little of his value, and that's not what he'd have wanted the timeless/updateless decision to be, of people in his position.

Cool.  Next up, make weapons for Cheliax.

...aaaaand his brain's not buying that one either.

Dear brain:  You must, in fact, either make weapons for Cheliax, or not make weapons for Cheliax.  To take neither of these options is not, in fact, among your options.  So you should decide which of these two things is better, and then do that thing, and then not feel bad about it.

If that argument doesn't sound appealing, is it because there is some additional thought Keltham is supposed to think, to weigh, before deciding?  Please exhibit it, brain; or make a gesture in its general direction.  Or throw up a tiny note of discordance or something.

...is he actually reluctant to make weapons for Cheliax mainly because his brain still hasn't gone quiescent about the Conspiracy thing?

This is not a very consistent attitude to hold, brain!  In the sort of Conspiracy world where Cheliax does not already know all of that stuff Keltham knows, where his making weapons would actually matter... Keltham has also been teaching them to refine spellsilver at 10% of the cost.

That is also a bad thing to do if he is secretly captive inside a Conspiracy!

If his dath ilani sensibilities don't instinctively worry about that, the way they worry about crafting weapons, it means his sensibilities are wrong and incoherent about at least one of 'Is it okay to make weapons for Cheliax' and 'Is it okay to mine cheap spellsilver for Cheliax' and he needs to resolve that.

Is he, in fact, thinking about the right things at all, here?  Maybe if he asked Lrilatha about weapons, she'd say it's unlikely that Cheliax could really benefit much from them, that he should spend his next effort on forging, or roads, or agriculture, instead.

Thaaaaat seems unlikely to be the thought that finishes this dilemma.

He has not, for one thing, actually asked about weapons.  Except of that paladin, on a much more grand and impractical scale of explosions that seemed safely nonthreatening to his real life.

And for another thing, explosives shouldn't be very hard at this level of chemical expertise, compared to mining spellsilver.

And for another nother thing, back in dath ilan, if he'd come across an internally inconsistent thought like 'It's okay to mine spellsilver for my apparent hosts but not to build weapons for them', he would have considered that as a big deal, and tried to resolve it.  He somewhat got out of that habit due to Golarion making him be totally incoherent all of the time.  But things are settling down now, he is not having a new terrible epiphany every four hours, and he can afford to maybe start being a little coherent, again.

Right.  So.

Is he, in fact, inside of a terrible Conspiracy of terrible people doing terrible things, who should never have been given any of his chemistry ideas and definitely shouldn't be given explosives.

Take a moment to experience fully how much this feels like an awful stale thought you don't want to have to think again...

And set that aside.

Okay, so.  Now that he's thinking about this clearly, there's obvious things he could do, which he has not done, and that would be a reasonable reason for his brain to fail to go quiescent about this.

One, he could actually try to review all of his evidence and compare the most probable Ordinary and Conspiracy worlds implied by that evidence in hindsight, to that evidence and each other.

Two, he could try to poke and probe at his reality in any number of ways that he has not, in fact, really allocated a special day to do.  Except this should actually be Step One because you'd want to do that before assembling all your evidence.  Only there's a preliminary Step Zero quickie evidence review that he ought to do before he assembles 'poke and prod' procedures.

Three, depending on results of initial poking and prodding and the evidence review, he could do things like try to do scryed consistency checks on the larger world, even accepting for now that it's dangerous for him to step outside Broom's god's interdiction.  He could ask to talk to somebody Lawful Neutral or Lawful Good who's powerful enough to demonstrate, like, their not being fake, somehow he is not sure of how that could work.  He could demand a huge assortment of random books from all over the world, now that he can afford those.  He could try in other ways to put his vision clearly outside of Cheliax even if he can't put himself outside of Cheliax.

It's not going to resolve any doubts about his having landed in a competent supercivilization that could keep him completely deluded.  That’s probably why doing this hasn’t seemed worthwhile to him before now.  It's not going to make his fears go away.  But it could maybe resolve his doubts about whether making explosives for a weaker putative version of Cheliax seems okay.  The Conspiracy that can actually be helped by him, if he makes explosives putatively to help Ordinary with their long grinding war with Nidal, is a narrower concern to investigate.

Even if Lrilatha said Cheliax didn't want any explosives, he obviously ought to do that just about the spellsilver business.  Really, arguably, should have done it before, but on arrival he was still disoriented then on a level where that would have been hard... and then he was too busy making spellsilver.  Yeah, in retrospect, there was sort of a missing step in the middle, there, had he taken time for meta-thought to order things.

Keltham doesn't feel too terrible about that part, it legitimately took a while for his brain to quiet down and shake itself out to the point where its remaining doubts were this easy to go through and organize, without a hundred other Additional Questions running off in all directions.

Still gonna suck if Carissa, and Yaisa and Asmodia and Meritxell and Ione, all get lost to him over it, after he let himself get attached... okay that problem is mostly Carissa, he'd survive losing the others.

Is his brain actually worried about that?  On a short-term timescale?  This requires that his brain assign significant probability, not only that everyone he's come to have feelings for is a Conspiracy agent, but that Keltham has enough evidence to figure this out, or will be able to find enough evidence as soon as he tries.

Well, that sure seems like the sort of thought that could get in the way of a happy relationship.  That makes Keltham's correct course of action here very clear.

He's going to announce now that he's taking tomorrow off announce that part tomorrow, it may inconvenience others but he doesn’t want his brain thinking that the Conspiracy successfully deduced what that request meant in context and stayed up all night to prepare.  He’s taken days off before, but maybe he’d ask for this one with a facial microexpression that gave it away, or somebody would make an inference from the precise timing of the request.  If he’s doing this at all, he’ll do it with a pretense of security mindset, so his brain doesn’t think he could try again better.

He’ll spend some time tonight figuring out what to try, and which spells to request tomorrow at dawn.

And then he's going to try to crack the world he's inside, to see if it's just a fragile eggshell, after all.