“There are a variety of reasons this proposal is unrealistic. Most immigrants probably don’t owe any back taxes, either because they’ve already paid them or because their income is too low to owe any taxes. What’s more, figuring out a tax-dodging illegal immigrant’s past income is a more or less impossible task. It’s not like there are extensive records on off-the-books wages.”
The taxpayer is guilty until proven innocent, and that takes solid record keeping and representation to prove. No records? The taxing authorities are free to, and they will, impute large incomes. The ensuing taxes and penalties (not to mention simple failure to file which is itself criminal) will quickly be a mountain. Then, the interest and penalties continue to compound.