If people in premades can't be matched with people who aren't, that means you can't queue as 4, and going as 2 or 3 will be much harder. Even queuing alone will take longer, because you're taking out a significant portion of the potential matches.
I'm sorry you've had bad experiences, but that isn't the norm. I find that solo players tend to be MORE toxic-- I've matched with a few premades that were actually among the nicest people I've met in the game. When I'm with a premade myself, we frequently encounter players who get angry over the smallest things and stay that way the whole game, even though we're staying calm.
I really think you're casting out a stereotype on something that doesn't exist. Most people are perfectly fine when playing in premades. It leads to calmer, happier players because they'll generally have a stronger line of communication with some of their teammates. They often won't type, because they can speak with some of their teammates through another means, but pings are still fairly frequent.
Again, you're making claims that most people can't corroborate. Your personal experiences don't match well with the majority of players, and even if they did, you'd be making things a lot harder on new players.
I propose a compromise. Keep the normal queue as it is now, but add a solo-only Normal queue to complement it.