[null0pointer]

A lot of people are equating this to theft. While I can see their point, the concept of ownership in bitcoin is closely tied to control of the private keys. In this case many people control certain weak private keys so in a way you are giving your money away by sending to these addresses.

[ryan-c]

Taking money from someone who did not intend to give it to you is a dick move, regardless of legality or technical difficulty of doing so.

[tylersmith]

If it can be taken, somebody is going to take it. It can be people that intend to keep it, or could be a person to intends to give it back. If you left a bunch of money unsecured, which would you prefer? Not having it taken isn't an option if you use a weak key.