Forbidding users to use your service to propagate "litte bobby tables" pseudo-pranks is likely a good choice.

The choice is different if like most apps you are almost only a data sink, but if you are also a data source for others it pays to be cautious.

I think it’s more of an ethical question than anything. There will always be pranksters and there will never be perfect input validation for names. So who do you oppress? The people with uncommon names? Or the pranksters? I happen to think that if you do your job right, the pranksters aren’t really a problem. So why oppress those with less common names?