Yeah, there are many legitimate reasons to prefer Mac to Linux or Windows, not the least of which is that Ruby gems just work better on a Mac because they are developed there (regardless of whether you will have to figure out those problems when you deploy to your Linux-based production environment in AWS :P). The issue isn't whether you use Mac or PC but in the holier-than-thou attitude about it. You are recruiting a team of (potentially) one-trick ponies who are religious about making judgement calls.

Probably a looooooooong stretch from just saying "Justify a PC" to you are building a uncompromising team but I would just say "The Best Equipment (We mostly use Apple)" would accomplish the same goal with less annoying language