Many sites? I've been blocking GA through ghostery for years and haven't had any problem ever. Only problem with Ghostery i've noticed is blocking Adobe Typekit and some other UI-framework i can't remember the name of, and that is extreeemly rare. Besides, as many others have said, if a site is stupid enough to rely on a third party server for analytics that is their problem, not mine, there are plenty of good analytics alternatives that can be hosted by yourself easily, and there are plenty of good websites out there that i can visit instead if one is not working without GA.