Is that true for intentional tax evasion? Certainly I've gotten a letter in the mail when I've messed up my tax return and owed money, because it was a simple mistake. But when it's clear that someone is doing something to intentionally not pay a tax that's owed, I don't think we should expect law enforcement to be polite about it.

Not if the state thinks you committed a bigger crime than just making a mistake on your tax form.