Blocking someone should not hide messages in normal game champ select.
When you play a lot of normals and have a decent win-rate, you run into a lot of the same players.
So, recently, I've been placed in the same games as someone that I guess eventually blocked me, for some reason. Some message shows up in the chat saying, something along the lines of, 'this player blocked you and can't see your messages'. But before this message even shows up in the chat, I call jungle (as you have to be quick in normals). While I read the message the player who blocked me picks and locks a jungle champion and picks smite. At this point, what am I going to do? I can't really blame him as he didn't know I called jungle.
Then the next time I get matched with him. He has several people blocked out of the four other people in the lobby. And the same thing happens again. So I pick support. When we get in game I say something like 'I call jungle and someone that blocked me picks it'. And he responds saying something like he blocked me and that he can't see what im saying, in a passive aggresive way. So I know he didn't mute me. My ADC pings me to go cheese in the bot tribush. I follow, and my jungler says, in all-chat "care bot tribush". The rest of the game, I don't really say much in chat, I wanted to win, so I helped him out when I saw fitting. It was a stomp-kind of game, in our favour, but he still continued saying offensive comments which I didn't respond to.
What I'm trying to get at is that he was using the blocking tool to assist him in getting his role and be oppressive towards players. The fact that he had multiple people blocked in one game, and doesn't mute them when he gets into game, show, to me atleast that he doesn't actually use the blocking tool to make the game less toxic, but rather the opposite.
I would like to say that you should be able to block someone from writing not friendly messages to you. But in normal games, you can't effectively call a lane without messages. Usually when someone picks a lane which someone else called, there's someone dodging, or two people in the same role. So even with no ill intent, someone having blocked someone else can lead to toxicity.