Not stolen.

They should either automate sending back the SBD with a memo, SBD not accepted, someone should help them do it.

or

Process all transactions once a year

or

Activate the SBD:USD trading pair.

or

Wait until they get sued, or feel enough public pressure to do something about it.

Making posts calling them thieves is more likely to get them to do nothing until they get sued than be compassionate with people who made mistakes.

It would have been great if your post showed what they respond to people who tried contacting them.

Many of these SBD were sent from Bittrex, it would be a mistake to just send them back without knowing the account ID.