See, it *has* been declared illegal, and the reason it is tolerated is that releasing unlicensed series, while feeding the masses of people who will never buy a disc in their entire lives... it also gets some (and enough to be profitable) people to buy the DVDs and other paraphernalia of their favorite series, whether manga, anime, artbook, or plush toy once they come out
And some series/companies DO hunt down illegal fansubbers, especially if what they are doing has a negative financial impact. So while fansubbing remains a positive boost to the anime industry, once it becomes negative in parts (post-licensing, direct ripping of the full DVD in high DivX or full DVD iso's), they will attack those parts, as they do now. Once/If it becomes negative as a whole, trust me, the crackdowns will accelerate.