Why have a report button at all in an automated system?

People have different tolerance levels towards toxicity and toxicity levels change depending on who you play with.

Some people may be more coarse when playing with friends as that's how they talk in real life together. If no one within that game finds the speech offensive, then they won't get punished for it.

Because it's not automated, people who are not reported for flaming do not get punished.

Well, for one, a fully automated system would almost certainly receive some degree of backlash, as well as potentially having some increase in false-positive punishments (if the system is just actively looking for cases to punish, it may just find behavior that ostensibly fits and punish without second thought.)

To that end, requiring a report to be filed is a mitigating feature, but reports also serve to allow players to decide what they believe is over the line in terms of behavior. A report is a player's way of telling Riot that they don't agree with the behavior a particular player was showing, and consequently, gives Riot (through the IFS) a reason to check if that player was misbehaving.

As for report-calling/report-rallying, that in and of itself can be a punishable behavior, since the IFS only needs one report to review and punish a player - and I don't think that blaming a loss on a given person and calling to report them is acceptable, even as a one-off thing. People who exhibit those types of behavior will generally learn to stop when it catches up to them.

because being reported doesn't do anything as long as you actually didn't do anything wrong

I feel that the system will punish when no punishment should be given.. If one person has an argument with another, why should that result in one or both of them being banned? Because someone got offended? What is the point of a language filter if you will still get punished for language? Why have players banned because he had more than one “trigger” in his lifetime of playing? This ridiculous notion that you need to punish players for having human reactions is silly.

What contradictory arguments. Does the ToS state you're allowed to break the rules if noone reports you? In that regard if the system is automated then it should review every player's chat after the game to detect if they violated the rules...

Because if no one has a problem (no one reports) then why punish people?