Well, if we're talking about the same thing, there are laws that the banks and fintechs are bound by. These carry hefty fines for the bank and potential jail terms for their employees if not followed to the letter, including things like providing zero context or information about why your account was blocked when suspicion of fraud or money laundering is raised. The failure to report suspicion is likewise punishable.
Do people feel that complying with the law is unreasonable, or do they feel like banks do other shady stuff in the name of compliance?
The (AML and some KYC) laws themselves are unreasonable for two reasons.
First, having access to banking and payment services are necessary is many places so much it should be considered a basic (human) right on itself.
Freezing someone's money or access to banking services could cause much more issues or more harm to some individual than some of the criminal charges yet it is done automatically without any proof, reason, any way to appeal, by the sole discretion of one of the stakeholder (without any independent third party). Which in spirit is going against the innocent until proven guilty (and probably even the right of fair trial and right to property human rights).
From people's perspective banks have more power and can easier "take" (freeze for months/years) your money than courts and have way less responsibility or oversight doing it.
Second, banking services is one of few which is nearly entirely depends on trust. If a bank (from my perspective) "can not" (not allowed) to account for every penny and every transaction then my trust in that bank (or even in the whole banking industry) is lost.
That is bad for the bank (they will loose customers), bad for me (because I must use more cash), bad for the society (because more cash would increase tax evasion and black markets, and because it lowers the trust in public institutions), just because some stupid algorithm thought that paying half the dinner to a friend would significantly help the finances of a terrorist group.
I'm not familiar with the exact regulatory text for fintech, but it's highly likely that there is a difference between suspended and closed accounts.
While it may be illegal to close an account without providing proof, it seems possible to soft-block or suspend an account for 'security reasons' without disclosing whether it's related to fraud prevention or other issues.
It's not illegal. Even though having access to banking is absolutely essential to every imaginable business, bank accounts are still treated as a voluntary business relationship by regulators. Some protections exist in the EU for individuals, but for businesses, it is entirely at the discretion of the bank to open and maintain a relationship.
Do people feel that complying with the law is unreasonable, or do they feel like banks do other shady stuff in the name of compliance?