There can always be unique situations, but as a rule - at least above the rec league level - this is absolutely NOT the case.

There is no way most (any?) parents can consistently separate the parent and coach roles. Either they are going to be too easy on their kid, or they're going to be too hard on their kid.

And even in the one in a million chance that they're perfect... the perception from others STILL has a negative impact on the kid, coach and team.

Bad idea. Every time.