I don't mind environmental kills when the damn map/round isn't based around them. Those obnoxious narrow bridge maps just turn into a game of 'who can guard break first?' It's just too easy to score a cliff-kill when there's so many obvious opportunities for it and I say this as somebody who does it an awful lot himself.
I try not to if I can help it but if I suspect they're lining up for the same thing I usually preempt that.
When I say this I don't mean I just go for the cliff throw but instead that I put myself into a position where a cliff throw is less possible or cannot be achieved with a single Guard Break or pushing ability and will see if they try for it. If they do I have no qualms about pushing people off the edge in a duel or a brawl. Dominion and Elimination is free for all for me since it is a race to eliminate enemies as fast a possible.
No, environmental kills are dumb, considering they give an advantage to certain characters who are able to just take you off the map even if you have good positioning, aka the Warlord.
At least in duels and brawls.
Dominion environments kills are fine, maybe even skirmish.
But in the more "skilled" gamemodes, environments shouldn't give an advantage to a player. Those modes everyone should be on equal ground, only difference should be how the characters play and movesets.