I’m not depressed (at the moment, well maybe a little), just feeling philosophical.
Edit: the idea of this came to me because I was pondering why people fight so hard to beat diseases and live a few more years. What are they planning to do? Why exert effort just to be here longer when you don’t have a reason?
Just why?
Open individualism is extremely similar to what you’ve described. I have a hunch that something like this is the case, though I’d stop short of calling it a belief.
There’s some good discussion on /r/OpenIndividualism.