Wouldn't really deter mass freekillers. The 30 minutes (or more) of red team does give enough time for new players to get a basic grasp of the important rules that are more unique to the server, though. Like hitting any guard results in a permanent rebel status, and no rewardening. So this would help a decent amount with the clueless players that aren't there to cause trouble but then end up forcing freeday or turning on ff accidentally. As for freekillers though, you can see how they would probably be willing to wait 30 minutes to mfk, and them "learning the rules" during that time has no effect because they came to the server specifically to mfk.
People are saying this suggestion would "kill the playerbase," which I don't really get. I regularly struggle to join the server because of it being jam packed, so I think we have a pretty good supply of players. And if someones not interested in taking 30 measly minutes to learn the rules of the server, why would we want them on anyway? It's like when an obnoxious person tells a fast food worker "you just lost yourself a customer," like.... thank god, yes, please leave. But yeah, I think this would help a lot more than hurt.