Your argument makes no sense because no one said the ninja mine is okay. When it is sold, then the bad action has been done. Ninja mine for profit = bad.

But the person who bought the stake is not responsible for the actions of the previous holder of that stake.

If I sold you 1000 Steem and was abusing my stake, upvoting myself 10 times a day, does that mean that you should now be downvoted by spam preventers?

And to answer your car example, if the car was sold illegally, then yes, it still belongs to the original owner. However, if the transaction was completely legal, then it belongs to the buyer. Other problems are not his to deal with.

Tron acquired their stake fairly.