AN specifically told us that Purity is harmed by Legitimacy and RA hits. The "rip out" option is a RA and Legitimacy degrading option that specifically targets people identified as puritans. I can't even imagine how anyone saw that and deduced that it would reinforce purity.
The real danger is that it might harm our justice value through disproportionate response.
I believe you have the cause and effect backwards there. It is not that lowering RA and Legitimacy hits themselves work against Purity. Rather, it is that the only options that work against Purity's downsides will always cost RA and/or Legitimacy.
Which tells me that just Cracking Down only stops the current outbreak, and does nothing to actually improve matters regarding the downsides of Purity.
As for the vote:
[X] [MP] Trade Excitement (+10 Wealth, +1 Stability from Guild demands)
[X] [Int] Attempt to tear out these maniacs, root and branch (-2 Intrigue, -1 Stability, -1 Legitimacy, -1 RA, ???)
[X] [React] Need more scouts (Sec More Blackbirds + Sec More Spiritbonded)
[X] [Ext] Find out more about what the Highlanders are up to (Main Trade Mission)
[X] [PSN] Main Expand Forests (-2 Cent + Costs)
As much as I dislike taking temporary bonuses over the potential for something more longterm, I think taking the wealth bonus is the best choice here. As I do not believe that the Crack Down option does anything to actually prevent Purity from continuing to be a problem long term, there is no real option other than full burn IMO. I'd much rather go into a confrontation with that aspect of society with full ammunition, especially stability.
Additionally, as much as the possibility of gaining loyalty is good, I don't trust the odds on that. No way to tell if it will help anything at all.
Getting more scouts, as has been said, puts us in good shape to take care of several other problems next turn, and in particular I believe that getting Cavalry better quickly is imperative, considering the way nomad's are developing. I fully expect us to need a minimum of 10-15 Cavalry to be able to face the next horde on equal-ish terms, if not higher.
While I do agree the individuals involved in the trade mission are at significant risk, we do need to know what is going on there in better detail. If the whole mission dies and generates no revenue, getting intel on the situation is worth the price.
Finally, I think we can afford to only expand forests, for PSN. The upside of the cashout from the Bazaar is that we can stay ahead on Forests in the meantime, without going broke.