There's nothing wrong with it, unless your deer herd is hurting for numbers. Actually depending upon where you are, it can be a better idea than shooting mature does for controlling populations and improving habitat.

Annually fawn requires more forage to grow to full size than a mature deer requires to subsist on. So if your habitat is hurting and you need to reduce the deer population, shooting a fawn is a double-plus.

Here's a somewhat informative article from the QDMA org folks:
http://www.qdma.com/articles/details.asp?id=46

If you've got a thin herd and your wondering where all the deer are though, you might want to tell your buddy to let a few of the small ones go.