Running for President is not something to be taken lightly. It should not be viewed as a publicity stunt or a brand enhancer. The integrity of the person running for office should be someone of proven integrity. Tax returns will go some way to assuring that whoever runs meets those minimum qualifications. Congress isn't forcing someone to reveal their tax returns. Anyone who doesn't feel comfortable doing so, need not run but Congress can set whatever standards it choses in deciding what information a Candidate must disclose to be eligible to run. Running for any office is a privilege not a right.