True, but its a norm that has been obeyed by every President in modern times (since Nixon IIRC). The public have a right to know if their President is financially beholden to foreign interests (like Russia, Saudi Arabia for example) which would be revealed in his taxes. At the end of the day its about basic transparency to prove one has the integrity to work in public service, which is not much to ask for. The fact that he is fighting so hard to prevent his taxes from being made public, only makes people more suspicious of what he's hiding, especially when his behavior has been incredibly complimentary to leaders in countries where the Trump org have business interests.