I don't think there's a stigma. It just tends to be more efficient for everybody within a specific production to be working on the same system.But if you have the skill to tear apart and repair machines they why not just build a custom machine in the first place exactly as you want it and save a boat load of cash in the process? That's what puzzled me at first. But like another poster mentioned, in some places there is a stygma of being a noob unless you show up with a Mac so I guess people in that situation have no choice but to spend the cash. I hadn't thought about that. Plus for some reason I thought you could run FCP on pc hardware given that Mac and Pc hardware are so similar nowadays. For example I have friends that will by Mac hardware and install Windows 7 on it, I oddly thought the reverse was possible as well, my mistakeI don't use FCP and my business partners could care less what hardware I use so I guess I'm more flexible in that regard. Note, I have no interest in turning this into a tiresome PC vs Mac debate, I was just genuinely curious why some are stuck spending $5k on a 12 core machine when I could build one for ~$2.5k. Makes more sense now so I'll step away...feel free to resume discussing the new machine.
So if you are going into a production that is based around FCP, it's just going to slow the workflow down if you are bringing a PC into the mix, even if it is just slightly.
The same is true of bringing a Mac into a PC dominated production.