Why many players are so upset about Boosters/Smurfs?

Hi, everyone. I wish to start with a quote: " To know your enemy, you must become your enemy" Sun Tzu.
What puzzles me ,is the fact that Boosters/Smurfs(B/S) are an extremely negative "factor" in most of the players' games. And let's be honest – it's only when they are enemies. But why is it so terrible to face a better player than yourself? Isn't this a free, individual coaching session, that only has to be analyzed by other players? You not only can see a proper way of snowballing and managing your resources, but you can directly identify your own mistakes ,in a particular situation. He isn't cheating, isn't scripting, isn't stream-sniping. He just uses his time more efficiently, he just capitalises on a slight advantage better etc. What I suggest, and firstly to myself, to watch the game against B/S. Maybe even if I played good, then to give a though:"what if the draft was bad? But he played average".
Another question to those who complain about B/S. If you can't let yourself to lose few games per several weeks to B/S, why there is even a player who is that much more skillful than you? I mean, if you are so serious about the game, you should try to be better in it.
Recently , I've played against a smurf on Tinker. I was on my successful pos 1 hero and lost. Managed to prolong the game and pretty much played normal, killed the smurf several times. eventually after the loss , I blamed him of being scripter, due to one suspicious hex of my teammate. So we started to discuss , waited for reply etc. I was wrong. But in the process he recommended me to have a complete different built against these heroes. And I was thinking about it, but not so much. So I learned that I could build agh's + refresher in late game with Luna, instead of buying satanic + skadi which I never used because of Faceless Void + Tinker. We actually couls win this game, but we had bad communication with team.
So my point is, I'm trying to learn from B/D , to think from their perspective, and so I recommend to you too. This is a live lesson.