If you just think every instance of gb trolling is bad then I can respect that, but saying stuff like "it doesn't matter in shooters but it does in a MOBA" is horribly patronising to the people who take shooters seriously and I can't respect that.
That is not at all what people are saying.
The thing people need to realize is that if you die in a shooter, most of which are 8 on 8/16 on 16 or more than that, it doesn't really matter. I can think of two ways of intentionally griefing in your standard shooter (obviously there will be variations of this but in general):
1. Killing your own teammates. This will probably get you kicked from the game eventually. I don't play a lot of shooters these days but it seems reasonable that that would be the case (it was in Counter-Strike when I played that).
2. Repeatedly dying to the enemy on purpose.
Neither of these give the enemy a huge advantage. If you have a good player on your team, or your team is just better overall, you'll probably still win even with one man down who's doing no good.
In DOTA, this is not at all the case. Every time you die to the enemy, you give them lots of experience and gold which makes them stronger compared to your own team. If you keep doing this, the enemy will get stronger and stronger until you just won't stand a chance in fights because the enemy simply has more gold and is higher level than your team.
Notice how this contrasts the shooters; dying in them gives the enemy no advantage other than being a man down. As I've said already, one or a few skilled players on a team can easily weigh up for this deficit by getting a few more kills every for death on average. In DOTA, this is not possible because the experience and gold you get from kills far outweighs what you can get from just killing creeps and neutrals. Of course, considering the case where a team of 4 pro players going up against an 5 average-skilled opponents, and a feeder in the pro team, the pro players could probably make up for the difference because they're simply that much better. But when it's a 5 on 5 with all players being roughly equally skilled? No chance.