It’s not illegal to have coins that at some point in the past were mixed. In fact I suspect that most bitcoins can be traced back to a mixer if you go back.
Perhaps, but as regulators step up it’s going to devalue things once people know coins from tainted chains are going to be harder to resell. That’s going to further increase the risk of using mixers since the people using them for ideological reasons are going to scale back their usage as it starts costing them money & adding risk.