A spike CAN become an impressive racked buck. I read an article on it in Deer and DeerHunting a few years back, and they have penned spikes that turned out to be big racked bucks. Also, there are some spikes that have inferior genes. My understanding is that the spikes who will always have a poor rack are far fewer in number than spikes who can grow bigger racks.

Your friend wants to let small bucks walk, but will shoot spikes because he doesn't think they will ever grow to be big bucks. Therefore, you need to educate him that this is not necessarily true. It isn't like he said he just wants to shoot something legal, and a spike is legal. He WANTS to practice QDM, and needs to be informed of the facts on spikes so that he can better get where he wants to go.