There's a lot of reasons why people will respond negatively to someone deciding to excise themselves from reality, and part of that is because there are a lot of different types of people, but we're almost all of us inherently social creatures.
Some people may feel sad that the person who ceased to be didn't think to reach out to them, or didn't clarify what was going on. This often comes with a strong feeling of guilt, a feeling that the former individual was let down by their friends who 'should have seen the signs'. The signs can however take many forms, and be easy to miss.
Some people may feel that life is so amazing and wondrous that's a straight up insult to discard it. Anyone doing so is almost invalidating their optimism, and it feels like a personal attack.
Yet other people, much like the first group, will feel like they were indeed given up on, like they weren't given the chance to support the no longer present individual. A slightly different perspective that can feel like disrespect.
Finally, there are people who don't want to acknowledge the option even exists, and anyone who uses it is making it more real. We want it to be so last-resort, that it's never considered an option.
At the end of the day though, it's always a permanent solution to a temporary problem, no matter how big. If you're really considering it, you've spoken to the helplines, tried to get the support of all your friends and you're out of ideas, sell all your shit, hitchhike 3 states over, and spend 3 months trying to live there. You literally have nothing to lose, and it's worth trying every fix before making what is literally the last decision you will ever make.
Correct. If an American can't do it, James Bond will. :)