> How do you know it's for human trafficking?

It's a thought experiment. There are surely cases in life in which you know for sure that crime is being committed. What you're asking for though is that due criminal process be a part of denying a payment. Which seems extremely heavy handed.

If my payment processing company doesn't want to help sell guns, or help with human trafficking, or hell, doesn't want to support the meat industry, then I should be able to run my business according to those ethical choices. My company isn't sending someone to jail. They are just refusing to accept a payment. There is no need for due criminal process to refuse a payment.

Should it be illegal to start a vegan payment processing company?