It is easy to prove that somebody is Smurfing...and you can by sight/within the first 30 seconds of a match. See that guy doing aerials in Silver? Maybe check his account. Does he have a Pro tag, 70% win percentage, and 5 alt accounts?

How many times would a Mod stumble upon that situation if they played 10 matches in Silver?

Let's assume that there is no way of policing Smurfs...why would Psyonix enocourage us to report them and supply a Report button if they never intended on doing anything about it (or addressing it publicly?). You can have one, but it's hard to explain the other. If they did intend on taking action against Smurfs/Boosters....where are the outcries of the people who got banned and "it was my brother who did it!"? This subreddit and the official forum would be full of those (like it was when they cracked down on swearing/KYS).

I personally know somebody who was banned for swearing. Ive never seen anybody banned for Smurfing. Right or wrong....Ive just never seen it and I think we would have noticed the "I just like to play games with my noob friends and they banned me" posts.