He may make 50$ per month but he must pay at least as much for power
That's right. Even a single GPU running for a whole month will cost you $10+. You'll buy a $1000 PC and have it running all day mining and buzzing. You won't be able to use it for much. After a month you'll get $40 back, great. Is it worth it? You could get more than that by using this PC to write articles, trade or something.
You're not quite right here. I'm writing this from my PC that's mining right now with 3 GPUs and CPU and has a shitton of other programs running. I guess games would run rather slow if I run them with my current setup (monitor is connected via onboard GPU) but then I'm not a gamer.