Does everyone eventually sell out or do they just start with ulterior motives?

One of the things that's been bumming me out lately is that one of the health blogs I used to follow religiously, especially for its clear-eyed view on the attack on natural remedies, recently completely turned me off with an Obama "birther" reference (yes, irrational). And autism blog I used to scan is now being used to shill one of the blogger's Kindle single romances (i.e., nothing to do with autism). Even Dr. Mercola is pushing his own products pretty hard on his site...

Of course, I run ads on GreenFertility, so I'm not 100% pure, either. But still...