It adds more toxicity than it helps. If you don’t accept the swap they very often troll, afk or soft/hard int.
It is a net negative at least with non-premades. So keep it for premade party members.
If the counter argument is counter picking then we can use the good old logic that the games will statistically balance out, while removing the toxicity from trading.
Do you even know what jungling is? They know the buff is shared and they troll a lot less because of buff stealing. So they do care, and a lot actually.
Also you said that swapping was added beacuse of toxicity, this is false. it was added to simplify the game, the champions needed, so no more chatting there. And with it came the trolls that refuse to play unless you swap them. That did not exist before.