I think their arguments is you went say eth->btc and then through a tumbler, they would be able to charge you for tax avoidance on the eth->btc (assuming you di

I think their arguments is you went say eth->btc and then through a tumbler, they would be able to charge you for tax avoidance on the eth->btc (assuming you didn't declare this and pay the tax) and then money laundering on the tumbler because it was meant to obfuscate that.