I understand why Riot punishes for "calling for reports" regardless of justification.
It's because it's designed to start a witch hunt.
Calling for them won't make anyone play better and actually makes them even less likely to cooperate. And it's clearly done in the nature of open hostility.
These two reasons are why it's against the summoner's code, thus a punishable offense.
I recently came across a player who insisted that calling for reports can't be punished because it wasn't in the report policy. Took me two seconds of thinking about it to understand why it's a punishable offense even if the reports called for are justified.