Contaminator,
You raise some interesting issues here. Legally and morally, of course, it is always wrong to infringe copyright; but the fact is it goes on all over the Web, all the time, so there's nothing much special about what goes on at this site. Since there's no practical way of stopping it, it will continue to be with us. Just how wrong it is depends on the circumstances.
The way I see it, there are three levels of "wrongness," depending on what sort of material we are talking about.
1) Material from free sites. No-one is actually losing anything here, except occasionally their tempers. Most owners of such material don't seem to mind too much, but in the case of those who specifically say on their sites that the material is copyright and may not be reproduced without permission (as JJJ does on her site), it's simple bad manners to disregard that. Apart from that, I don't have a problem with sharing such material.
2) Samples and occasional photos from pay sites. This is a bit "grey," but could be justified on the grounds that they can be regarded as being like trailers or adverts, actually encouraging people who see them and like them to visit the site concerned in search of more. Most pay site owners seem to regard it in this light - I myself have posted photos here from VN Longhair and never had a complaint. There are exceptions, of course. For example, Anya and Leona both object strenuously (as is their right) to ANYTHING from their sites being shared without express permission. I consider at a moral obligation, though, when posting this sort of stuff to credit the site it comes from.
3) Complete videos and photosets from pay sites (as per the request which started off this thread). This is a real no-no. These items are marketed products that people are selling, so to make them available on the Web for free is tantamount to depriving these people of their livelihood.
Basically, it all boils down to the old and simple rule of good manners: if you wouldn't like it done to you, don't do it to others.