Lots of credit card companies have restrictions on where they can be used. Cryptocurrency is an obvious example.

The problem is that there are a lot of laws around gun purchase, especially globally, and the legal repercussions (federal and civil) of an illegal gun sale can be a LOT more than the repercussions of selling illegal beer.

Here's the thing, and keep in mind I'm very pro 2a. It has nothing to do with 'oh gun are bad' 'oh drugs are bad' 'oh porn is bad' it does however have everything to do with 'high risk items lead to much higher chargeback/fraud rates and we'd just as soon as not deal with that unpredictability and general headache'.

That is why 'high risk' processors charge a considerably higher % and per transaction fee and generally hold a percentage (I've personally seen as high as 50%) of every transaction for 1 month or longer (I saw an extreme of one holding 50%, releasing 25% after one month and the other 25% after 3 months before releasing it to the business as you generally have 60 days to dispute a charge).

You are assuming moral reasons where simple business reasons suffice.

That’s why I said I hoped you were trolling, because the alternative is that you have a strong opinion about something which you have thought insufficiently about.