I would never be offended, but why daty with dental dam?

Kind of defeats the purpose & the pleasure.

.....nope wouldn't be offended at all just like I wouldn't be if a client asked for a condom before a bj.

I saw a girl who wanted me to use one.  It did nothing for me.  

Personally, I don't really feel CBJ either, so my thought is that, if it is as sensation blocking for the girl as it is for the guy, I wouldn't bother and would move on to either someone else, or some other activity.

But, we aren't here to judge.  If you like the idea of DATY, and don't mind licking plastic, or if you have a girl that really enjoys it, then go for whatever works for you.