I frequently sit on my balcony, with my MacBook Pro in my lap. I'm still alive.
I also frequently use that computer, that doesn't have vents on the bottom, for watching movies in bed. And I don't need to think about vents. My last non-Apple computer was some ThinkPad, with vents on the bottom, and I remember always chasing some book to put under the computer to make the vents free. Boy, how I hated that.
I doubt any computer you can life will kill you if you put it on your lap. It might be uncomfortable, but it won't kill you. (I'm not about to put some of VAXen I've seen on my lap even though I can technically lift them, but...)
People do all kinds of terrible things to their body. That you do something and seem to be getting away with it doesn't mean you should. Talk to a real doctor trained in this (your regular doctors probably is not) for details.