The issue - which has already been reiterated above - is that the Ts & Cs that the existing service operates under are changing to a far more restricted set.
Your argument kinda meanders around being a privacy nut and sticking it the the man, then you say you are not justifying a stupid agreement then you say all agreements at all sites are stupid anyway. I've no idea what your point is, frankly.
But you do say that the new terms are totally like all other social network sites. Well the old/existing delicious is a social network (as you state) and the new terms are very much not like the old terms. Clearly not all social network terms are equal.
Besides, if one cared much about that sort of thing, chances are that they wouldn't stop using Delicious now, because they would have already stopped using Delicious when Yahoo! bought them, for similar concerns over privacy and agreements.
Except that the Ts and Cs didn't change much when Y! acquired them which is why there was no need to opt-in like there is now.