I don't know anything about modern Quakers in Britain, but theeing and thouing is pretty much out in the U.S. Occasionally people use it around other Quakers, but mostly it's considered anachronistic, and sometimes it comes across as sort of pretentious. "First Day" is still in in Quaker settings, though (although we call it Sunday the rest of the time so non-Quakers know what we're talking about).

And yes, there are songs I won't sing because I really don't agree with the message. Some of them are songs I instinctively like, but when I listen more closely, I really can't sing them honestly. Run into that problem a lot because, musically, I love country-style gospel but I don't feel I can fairly sing about being washed in the blood of the lamb or waiting to understand it all by and by. (I'm an atheist--I probably shouldn't be singing gospel at all, but there are some whose words I like in spite of little God references.)

I hadn't thought about it quite like that, CapriUni, but now that you mention it, I would think it was disrespectful of others' beliefs if I did sing them as a "put on". I don't sing things to mock them, anyway, but I hadn't really thought of it in those terms.