I agree with the OP, if you get someone throwing racial slurs or intentionally trolling even in pregame lobby, a dodge is your best bet to avoid the outrage and frustration. Basically, I don't think dodging should give any punishments to rank at all. I agree to keep it from becoming a constant issue you should still get your wait time punishments for continuously dodging games and such, but still, shouldn't affect rank. And the OP is right, using the slippery slope argument is rather stupid and childish at the best of times. Simply put, don't make the game as frustrating as possible then get mad when people get frustrated, that's the childishness of Riot though.
Riots Mindset:
Makes Game
Game is good and fun
Then....
Makes game overly frustrating and gives power to people to annoy others
Gets upset that players get frustrated and toxic
Throws a power tantrum
"Don't get mad, be nice to the snowflakes"