I can tolerate waiting; while frustrating, that's not the real issue. But it's hard to just live a normal life in limbo, with all the implicit threats. Your documents are tied to your job, so switching jobs will risk, at minimum, starting from scratch; and there is a chance of denial and deportation at every turn. You are also not immune to layoffs, so this can blow up in your face without warning, giving you a very short period of time to fix it. And in the end, even if you survive all the hoop jumps, there is still a chance you will be denied the documents that you've been waiting years to receive.
Compare this to somebody just wanting to do essentially the same work in their home country, where they probably can, minus all the bullshit. This is why the U.S. is in danger: because immigrants can only take so much, and at some point, they simply will move all their ideas and capital back home.