I think the thread Mr Offer is seeking is this one.

I suppose this is a slightly different question demanding slightly different answers. My first comment would be "have to" - perhaps not but I think we all should try to do things to the best of our ability and perhaps if as El Greco suggested you are to be a professional earning a living you need to sing well...

The question of course is what constitutes singing well. My own comments on that side are in the other thread...