Does anyone (Darren/Luciaphil/others) know if there were fans/haters of show who wrote to TPTB about the way Maggie specifically was being demeaned?
Don't know about letters the show may have received, but there weren't any complaint letters published in any of the daytime/teen magazines.
It might be hard to understand nowadays, but depicting female characters the way Maggie is written in 1970PT was far more prevalent than might be suspected - particularly on daytime. While women probably wouldn't have behaved that way in real life (or tolerated the sort of behavior Quentin exhibits from their real life husbands), most viewers wouldn't have actually found Maggie and Quentin's relationship all that much of a departure from what they were watching on many other soaps at the time.
Another thing that should probably be mentioned is that at this point in daytime TV, one of the prevailing notions was that characters/storylines had to be larger than life, filled with more tragedy, more heartache, more disaster than anyone in real life could ever possibly experience. That way viewers would supposedly come away with the feeling that no matter how bad their own lives might have seemed to them, their problems were tame in comparison to the tribulations their favorite daytime characters were expereincing. You see this stated time and time again in all sorts of daytime articles from the period. Almost more than any other medium, the vast majority of daytime soaps were considered as completely escapist fare that was in no way related to real life.