If people could ensure that no one would restrict how others uses the program, having GPL'ed software released under BSD would not be an issue.
A bsd project could simply add to the license that people should not use patents, legal threats, or hardware tricks in order to restrict people, and I would see that as equivalent as making the whole work under the GPL. The BSD license itself is not a problem, but people who would abuse the license in order to add restriction is.
Thus, BSD products can use GPL code, but they can't enable those who want to add restriction to the BSD product.
If they must enable those who want to add restriction to the BSD product, then they can't use GPL licensed code.
If they don't care about enabling proprietary model for the product, then they can just continue license their code as BSD and combine that with the GPL licensed code. Distributors will have to abide to both licenses, but that is not a problem so long they do not try start a proprietary model or tries enable other to do it.
A bsd project could simply add to the license that people should not use patents, legal threats, or hardware tricks in order to restrict people, and I would see that as equivalent as making the whole work under the GPL. The BSD license itself is not a problem, but people who would abuse the license in order to add restriction is.
Thus, BSD products can use GPL code, but they can't enable those who want to add restriction to the BSD product.