Bradley is getting a long leash, because there are no other options. All of the internal options would be atrocious in CF, except for Victorino. However, RF in Fenway Park might as well be CF given how huge it is. Gomes, Nava, Carp, and Sizemore would still be awful, and still don't hit enough to justify terrible defense of that extent.
Bradley isn't even the worst outfielder on the team. He isn't even the second, third, or fourth worst if you count Carp. The options mentioned in this thread are not CF's. Ethier has barely played CF in his career, and he was awful when he did. Ethier is also potentially due 4/68, so you can cross him off. Denorfia is a cheap rental. He rates very poorly in CF, but he would be a nice upgrade in LF. Of course, we could always trade for Denorfia and Stanton, and go with a Stanton-Victorino-Denorfia outfield. Bradley could be the 4th OF for the rest of the year.