I used to play ARMA quite a bit and there is nothing more infuriating than someone playing the game using speakers, with a stand alone mic. Especially if they haven't disabled voice activiation and enabled push to talk. If you have 3 or 4 people doing it with voice activation, next thing you know you've got feedback loops on top of feedback loops on top of feedback loops, push to talk isn't so bad, but can still be a problem depending on how loud they have their speakers and the sensitivity settings on their mic. And then there's the people screaming at the offenders "DUDE! YOU'RE HOT MIC'ING!" every couple of minutes which is mind bendingly annoying.
Even a cheap headset is preferrable than no headset in those types of games. At least in my experience. And if I didn't have a headset, I wouldn't use a mic. I just set a macro to send "NO MIC" to chat or use the hot keys for the radio quips like "roger", "yes", "no" and that sort of thing instead. It means I have to remember quite a few more key combinations in a game that's already full of them, but at least I'm not that guy on a feedback loop on top of a feedback loop.
It's an absolute gaming pet peeve of mine and has been since playing Delta Force 1 in the 90s.