MGM Lion,

I may have been exaggerating or over generalising and accept that there will be some exceptions including those who may have some physical problems with their vocal chords or other disability.

There are, of course, many people who cannot sing very well and not everyone is going to achieve the same standard. That doesn't mean that they shouldn't sing, of course. Nor that they should either....
Also, what is pleasing to one ear might seriously upset another listener and, of course, we all have our favourites. Often, I may prefer to listen to somebody whom is not necessarily the best of singers but not enjoy another technically better performer.

Anyway, I think the vast majority of us are capable of making some kind of noise or other which could pass off as singing. We should all be allowed and encouraged to do so within reason. In the appropriate circumstances, of course. ;-))