The IRS is in the business of getting money for the federal government. People in federal prison don't have much in the way of income, nor do they pay much in the way of taxes. They're a net drain on the federal budget.
The IRS will generally take the most effective tack it can in getting the money it is owed. For honest mistakes, that usually means sending you a formal notice that it believes you are out of compliance and requesting that you pay them. If you pay them, all is forgiven. If you can show to their satisfaction, with supporting documentation, that you don't actually owe the money, all is forgiven. (I once got a notice that I owed $11K because of some stock sales I'd forgotten to report and education credits they didn't believe I was entitled to; after producing documentation on the cost basis of these sales, a course transcript from the educational institution, and an amended tax return, the total was reduced to $50, I enclosed a check for that, and I got a notice back that the matter was closed.) If you try to pull any funny business or argue with them and your arguments are not backed up in fact, they will viciously hound you until you pay the money that you owe.