"A little bit" of theft is not ok. And its actually against the posted rules of this website, though one of the longest and most active threads on this forums is all about this type of theft and actually was given XP by the owner of this site, so yea, it doesn't surprise me that this attitude is prevalent here. Funny thing is, this owner is actually an RPG publisher, perhaps he doesn't think piracy hurts his business.
As others have mentioned, site like the linked one, along with the free basic rules and SRD actually means that for many players they may not have the need or desire to buy the actual books.
But, the bigger point is that by accepting theft and piracy as ok under some conditions, makes it easier for people to justify theft under more conditions (too expensive, not going to pay if I don't know its any good, it doesn't cost them anything since its just a digital ciopy...). It leads to the devaluation of the property and similar works.
These views means that the work and effort by the people who create such materials is devalued ('hey,if I can get something that's almost as good for free...'). It means that many people who want and are capable of having a career in the RPG industry can't do so, because the customer base artificially lowers the value of their work through theft.