When you say mention "a service", are you referring to PayPal? In fairness, there are 0 payment gateways (as far as I know) that are open-source, sadly, so they don't have much choice. I guess the only option they have is Bitcoin, which they accept, however as that hasn't caught on they have little choice other services too.
So, when it comes to walking the walk, are you saying FSF is just like everyone else: free software is great, as long as it doesn't stand in the way of making money?
Without online donations, they wouldn't be able to raise as much money to support their campaigns. Personally I believe that it is worth it, just as it is worth using a closed-source machine to save somebody's life, rather than let them die for the sake of ideals. Of course the FSF would rather use free software to take donations (accepting bitcoin was an attempt to enable this), however by sticking to ideals in this situation it would harm free software more than it would help it.