Code under the BSD can be used in conjuction with GPL, so you are not excluding GPL people, but it can also be used with some licenses which are not GPL compatible. I would recommend against releasing it under the GPL and then telling people you will not enforce it.
Many people dislike the uncertainty of something like that.
If someone wanted to use your code with a non-GPL'ed program, these sticklers would refuse to reject or distribute the program, even if you had intended that to be okay. In other words, I'd recommend against specifying additional restrictions in your license if you don't want them to be there. It will either confuse people or make them avoid your code. If you wanted to guarentee something stronger than the BSD, then that would be one way. There is also dual-licensing and such if that makes more sense to you.