I would just try and educate him some more. Yes, a spike CAN become a much better deer. The majority of spikes are late born deer, rather than inferior deer. Deer & Deer Hunting did a series on it a while back that was good. Of course there is still no way to know what it will amount to. Bottom line is, it won't amount to anything but a spike if he shoots it.
Isn't Ohio a 1 buck state? He would want to waste his tag on a spike, and be done? I say if he wants todo that, let him. You hold out and shoot the big one

He'll come around eventually.