L-canceling is indefensible, yes.
But, now we have the matter of changing things.
If Isaac Asimov taught me anything, it's that there's social inertia to things.
Hopefully, some day, all Melee tournaments will be 20XX modded with auto l-canceling, and Project M will be auto-l-cancel by default. This might be far in the future because of the inaccessibility of Melee mods, and many players won't want to practice with something that won't be what they work with in tournament. But, that can be overcome, since they don't have to change their muscle memory at all, and if they can be convinced that it's just them playing at an automatically slightly higher level, it's just that all missed L-cancels will become successful, so they can just not worry about that.
That would mean those with access to Melee mods be at an advantage, however slight, since what they practice with be entirely consistent with the tournament experience.
Edit: There are two small fears, though. It may shift the favor too much in offense, for even the highest of players can be forced to miss l-cancel. How exactly, I don't know, it's just a vague fear.
The second is it could cause a division in the community, however slight, since some tournaments might be running it and some wont, so those who want to go to other regions / larger tournaments might not be used to having to l-cancel, thus just straight not want to go. Note, there's no need for a hostile cultural divide, it'd just be that players would lose passion for playing more broadly due the difference.