Thommy gets the bigger picture -- porn sites are commoditized but the user traffic is of value to others
If everybody gave away free widgets this does not mean there are no buyers for someone else's gadgets.
Unfortunately, much of the free commoditized content is also someone else's "stolen content." At some point -- there won't be anything left to steal. And at that point this scheme will collapse however the buyers are still going to be out there just somewhere else with a new content model.
An affiliate is just the contracted agent of the principal -- a sales referral agent. As song as the referrals are of a lawful nature -- money is money. Paid advertising is just another revenue model -- get over it. These are integral to building a content approval base of users -- branding.