>>7482905First of all, let's make it clear I'm not the brightest tool in the shed.
Anyway, I think it has to be the latter and not the former given that if that were the case travelling back in time would open up the possibility of you altering something that'd have repercussions in history down the line, and that could have effects, if not on your birth, then at least on the circumstances surrounding your raising or your parents', etc.
Basically, the mere act of going back in time (as opposed to jumping to a parallel universe) could create ripples that could very well alter the person you are and even the circumstances under which you created the time machine, or even though about going back in time in the first place, which is why the whole "kill myself" is the absolute logical extreme of things, since you wouldn't need to do that to screw over yourself an and create paradox, it'd be far easier than that.