very trustworthy of the system sharing your taxes with a third party

People's tax returns are essentially public (yes I know they're not allowed to disclose them). Didn't send the forms in with social security numbers.

This absurd concern for privacy is silly in my opinion. The moment something is submitted to the government it ought to be considered public. Even your social security number is essentially public for anyone who cares to find it.

I would not submit my bank account information to these services, or my passwords, obviously.

Honestly, tax returns should be public again. Would make everyone better behaved IMO. It was this way for most of American income tax history believe it or not.

To be clear, my information has already been part of several breaches anyway. What protects you ultimately is the law not information security. Of course this point is often lost on engineering / computer scientist types who don't understand how law works.