3 reasons.
1.) Nothing we can do on the boards would ever amount to anything greater then just reporting the guy in game. We an't riot and can't do anything productive about it.
2.) What we can do is invite a ton of unwarranted attention that a player might not deserve. Not only would things like toxicisity and death threats but also several illegal actions like hacking or doxing. And you and riot would be held accountable for what ever shitshow occurs.
3.) No one is perfect and the potential for innocents to be falsely accused is too real. If someone where to post a persons name and says he's a toxic person only those with access to the chat logs (I.e. Riot) would know if it's true or not. So not only is there a massive chance of huge mess that law enforcement might be dragged in to resolve, but it could center someone whose wholly innocent and thus damage everyone. The game, the players, riot, the forums, and YOU.
So no it's not a good idea to do this. In fact it's a really dumb idea. DONT DO THIS.