When will developers learn that the BSD does not protect you or your users? I understand the philosophical reasons some folks like BSD/MIT-style licenses, but at the end of the day they are not much more than public domain: anyone can take someone’s work and contributions, make improvements and keep the entire thing — original work and contributions, as well as improvements — proprietary.

If you care about a software commons, if you care about benefiting from the improvements others make to your own software, if you care about your users benefiting from the improvements others make: use a copyleft license!