Again, if this "implied guaranty" is so apparent as you imagine, why do the investors waste their money on paying insurance for the securities? Sorry to be so technical. The association with the government comes into play not because of an implied bail out back up, but because of the higher than average loan standards and, even more important, standards that are more consistent and unlikely to change at a whim, as compared to most investment banks doing anything similar.
In any case, regardless of the veracity or lack of concerning some 'implied guaranty,' the contention is that GSE's are at least partly responsible for the meltdown. The invitation is again extended to point out when in the 75 years of these programs prior to 2008 this has occurred before, and if so, if it was determined that GSE's were in any part the cause. Surely in all that time, with numerous housing market downturns, the GSE's should have done their damage at least a couple of times before now.
No one in any of the financial publications I have read mentions GSE's in the way of culpability at all, nor in any official or semi-official investigations into the financial disruption are they mentioned as even a partial cause. If it suits your world to have it otherwise, fine; if it is your opinion that GSE's should be done away with, fine; but trying to foist off ideologically motivated conjecture as fact to people who know better is just plain silly.