On the past few days I noticed a trend, the "it's ok to KS in LoL".
I understand the reasoning, it's securing a kill, not stealing. However, it's much more than that, it's distributing gold. If I'm 1v1'ing someone and someone else shows up and last hits, it's annoying but it's more gold for the team, kill + assist (singular) > kill alone.
But gold distribution is massively important.
I just had a nice ranked game where this was ridiculously evident. Playing Lux mid I managed to have more presence is all lanes than my jungler Diana (who also refused to give me any blue buffs). I was against a Malzahar, meaning that if I misplayed and the enemy jungler was nearby, I was pretty much dead.
I showed up top twice, both via TP when my laner was about to die. On both ocasions my Poppy toplaner survived with less than 50 hp and with a kill under her belt. One time I ganked top, got poppy a kill and then immediatly tp'ed bot and got our vayne another kill.
So far so good? Sure I'm not really ahead because I'm only getting assists (but losing minions) but at least I'm getting my laners fed.
My jungler didn't gank my lane once. She did show up mid, but only to take farm. When I'd save Diana (after stupid invades) she's smite to take the kill.
In theory we would be ahead, all players except me were getting kills, so naturally we'd be winning.
The problem comes when those guys you got kills (especially Diana) begin feeding when you can't save them. Going 1v5, trying to steal blue buffs even though there's a ton of wards and pings being spammed, ending up feeding a jungler and giving assists to Malzahar.
It then got to a point where I was 1/0/5 or so, which was when I started dying. Malzahar could just flash combo me, especially with Lee Sin. I couldn't ward everything, nor I could clear their pink wards alone (which I pinged to get help and got ignored for the most part).
In the end? In the end we had a glasscannon Diana getting 1 shotted even though she had half the team's kill, and a full tank poppy that couldn't peel for shit (including on two different ocasions ult'ing the entire enemy team saving them from my own ult).
In the end we lost because of ks. Sure we got kills, but the gold was in the wrong characters. The difference between me having Zhonyas and Ludens versus not having it is the difference between being able to burst the enemy team or just being able to CC up to 2 targets at a time. And when the one with the gold = damage is dead, you really aren't taking advantage are you?
In sum, while killstealing is harmless on its own, it requires the ones that are being invested in (not only kills, minions aswell, gold in general) to not waste that advantage by staying in one lane 24/7 while the enemy team 5v4s the rest of your team, or literally being useless because you'd get pulled every 9 out of 10 blitzcrank hooks.
Killstealing IS a problem if the person who is getting the gold isn't going to carry you.