When someone dies on your team, it's frustrating (especially when it's a feeder). However, the person playing it is a human too (unless it's a bot, but this happens rarely unless it's on intro bot and aram). I have been the feeder with a score of 0/8 at 20 minutes before. I realized I fed and didn't play well, however, I continued to play another game (which I think I won and stomped, but that was a little while ago when I was around p4 on my alt acc, which is d5 atm).
Not everyone is as good on one champion as they are on another. I could have been that 0/8 naut, but If I have went poppy, I could have been 6/0 in lane. Sure, me going 0/8 on naut was my fault (I honestly didn't play him back then, now I do) but that doesn't mean that I was tilted prior to this game.
People could try to be able to play new champions in ranked. I understand the statement of being playing in normal to be able to play it in ranked, but it doesn't work all the time. I might be able to know a few tricks on the champion and know the basics of the kit, but I won't be able to apply them as well in a ranked game.
Also, a death is technically worth around 400-600 gold depending on how much exp, farm, and tower you get (which if you get tower I guess it would be worth closer to 900). Your opinion about dying and tilting is your own, I have mine too :).