Because viral licenses get real terrible when you want to get features from two that are mutually incompatible. When two projects have different ideas on imposing "freedom" on users, it makes it harder to cooperate and make a better end product for the users. As such, I much prefer free as in free licenses like BSD over restrictive licenses like the GPL.
because GPL tries to reinvent the definition of "free" (I recommend consulting a dictionary, and than reading what GPL considers free/freedom, you are in for a mean suprise).