Toxic people are banned. They create smurfs and sice they dont value their smurfs, they plague pre-30 lv matchmaking pool with their toxicity. Yet other players create smurfs just to burn them, venting their frustrations with toxicity. As a result, new players will be subjected to GREATER levels of unacceptable toxicity than older players. This is horrible new user experience and is likely to dishearten new players.
AFAIK DOTA doesn't ban accounts for toxicity. Instead, chat restrictions, low priority queues and shadow pools are used. Shadow pool is when extremely toxic players (inters and the sort) are only being matchmade against themselves. While it is possible to find out if one is shadowpooled or not, this requires typing an obscure command in the game console - shadowpooled people are not outright told their shadowpooled.
I don't really play DOTA so I don't know how effective this is in preventing toxicity. However, **_if_** this is going to reduce toxicity among low level accounts, maybe this is worth it?
Make it harder to spam smurfs for circumventing rules. Ban people on MAC adresses for example. Yes this won't solve the problem and it WILL create more problems (innocent ppl banned bc they use a shared machine) but this WILL the "toxic smurfs" issue less rampant (though not solved in entirety).