Why hasn't someone tried to reclaim stolen bitcoins from current holders on grounds that they are property, not currency? I'm not the only one who sees this risk; I have seen legal experts raise a similar point.

If you steal money and use it to buy services, the person who receives the money can still keep it. If you steal property, such as a diamond ring, the person who receives it can claim it from any future owner. Bitcoin appears to fall in the category of diamond ring.

This would imply that if someone could trace a chunk of bitcoin stolen via hacking or ransom-ware to accounts at a large bitcoin exchange or service provider (e.g. coinbase), they could attempt to force the return of the relevant amount.

True, this may be very difficult and perhaps the costs would exceed the value of the coins recovered; however, the fact that such actions could degrade the value of bitcoin could tempt two groups of actors to try this.

The first group would be governments that are tired of police departments, hospitals, and other services being afflicted with ransom-ware attacks. The second could be investors who short Bitcoin and Bitcoin-ETFs, counting on a crash precipitated by the huge loss of value this could cause if people determine any bitcoins they are paid could be reclaimed at a later time.