Real fast. Bitcoins are network access  and certain network authentication services. The legal term is an incorporeal hereditament. Yes they can be stolen. Yes there is title to them. Possession alone passes no title even for negotiable instruments, which happen to construe possession most strongly.

There is no legal or moral excuse for this behavior. At the very least there is UNJUST ENRICHMENT which is a tort.

Anyone claiming otherwise is a fool and an idiot. You are so dependent on the nanny state to define your rights you forget them some rights are strictly sui generis.