I would much rather pick our own teams. For people who want to play but have no friends, I am sure we could find groups who are willing to accept other players. If random teams are picked, there is no guarantee I won't be paired up with a troll who throws the entire game, or someone who never even shows up in the first place. Additionally, I might stand no chance if I get paired with four other people who just want to play casually where as I actually want to have fun and compete. Randomizing teams would also ruin the skill of individual teams, the main point of CSGO is relying on your teammates to execute specific instructions reliably. Playing with people who you can't trust leads to a poor experience.
I understand that this is for fun and it is intended to get community members all together to have fun and play! However, I still think this can be done when allowing people to pick their own teammates. When we play ten-man games on Joey's server we pick our own teams and it's loads of fun. Half these people I rarely interact with anyway but the point is still there. Additionally, you'll be playing against people you might not know and adapting to their playstyle and interacting there, I think this suffices.