First off, let me say that I had a mindset similar to yours for a long time, and hated runs that abused death. They looked ugly and I didn't like to see them.
However, this is a speedrun. Our goal is not entertainment value. Dropping bugs and catching them is way less entertaining than actually doing the Shadow and Spirit Temples. Our goal is the fastest run possible. Whatever it takes, outside of gameshark or hardware manipulation or stuff like that.
There are constraints. Other than that you don't use gamesharks or hardware manipulation, you also don't savewarp in this run. With savewarping, you'd be even faster, but still you don't do it. You still put constraints on what's acceptable and what isn't.
So where do you draw the line? Why isn't it a single segment run anymore if I savewarp but keep playing? Why is it still a single segment run if I deathwarp and keep playing? Because you didn't go to the title screen, and that's the rules, but the rules are more or less arbitrary. We've added the constraint that you can't go back to the title screen in single segment even if you keep playing. We could just as easily add the constraint that you can't die in single segment.
I'm not saying that we should. I'm saying it isn't true there are no constraints at all.
For me, a single segment run with a death warp in it that saves 30 seconds on a single segment no-death run, isn't necessarily a better run even if it's faster, although a run with a new sequence break in it is awesome and makes me go "whoa, amazing!"