The claim is that it is a civil matter, and your fifth amendment rights apply only to criminal matters. Of course, that's pure BS. This is done not just in IRS matters, but in a variety of others.
Yeah and when file criminal charges what are they going to submit as evidence?? Your tax return, because you waved your rights when you signed it.
So the government tries to confuse the matter by splitting that Civil/Criminal legal hair.
The fact is you are waiving your rights when you sign a return and how the government gets away with forcing you to do so is an affront to good law and justice.
The government if they were wise would just do away with the income tax and go back to a sales tax. Then everyone would pay including the rich.