Junky - I think thats a fair comment over potential bias, but in the past I've volunteered with NCDL and a smaller wildlife hospital, where in theory our views couldn't be more diametrically opposed but we had a shared belief in the welfare of animals. and its probably worth saying that my ex and I met when she was an animal care student, so I'd argue that its not just a knee jerk reaction to anti's, rather a position I've reflected on.
I'm a firm believer in animal welfare rather than animal rights.
For what its worth, I know a lot in the field see the RSPCA as another 'charity industry' - rather than being led by results/improving the lot of animals.
Good programme a while back on R4: http://www.bbc.co.uk/programmes/b037v4fp