It does seem as though there is important distinction between merely being a pureblood family who has always refuses to succumb to anti-Muggle sentiments, and a pureblood family that rejects the anti-Muggle sentiments. For all the mistrust, the attitude toward the former seems almost "to each his own", and this does not lessen equality on either side really; before Voldemort's rise, we're given every indication that the Malfoy name is a powerful one with loads of influence, but we get this sort of implication from the Potter family, the Bones's family, and even Neville Longbottom seems to be well-off with famous parents.

Vitriol seems to be directed toward the only family we know of that has changed sides, and a fall from grace seems to occur when one does so. With the exception of the Gaunts (who we are told squandered their fortune), the Weasleys are the only pureblooded family that we know of who live in comparative poverty. I can't completely rule out the fact that if Sirius had had offspring, and started his own family, they would not have suffered the same "blood-traitor" backlash that we've seen directed at the Weasleys from families like the Malfoys and Blacks. Nor am I convinced that said hypothetical family would not have ended up in the same financial straits as the Weasleys had Sirius's Uncle Alphard decided not to give him an inheritance.