Refreshing thread. I was always quite surprised at the harshness and expectations that SM shouldn't complain despite the disproportionate sacrifices many make. I wonder if it's sneaking envy in some cases in acknowledgement that it is a tough job. There is definitely sexism at play too in that a SM is fair game but a SD is a saint.
In my case DSD was f/t resident, so I did the giving, emotional support, financial provision (house, hols etc) and bore stiff upper lip against occasional rudeness. Not perfect just my best, like most parents. As many have said if the resident parent ignores poor behaviour it undermines everything. And this has made things increasingly difficult over the years, esp now we have younger DS and DD, since DSD has become more vocally rude when visiting (living with bf the last couple years). DH will not confront her but rips a strip off our DC (15 years younger!) if they're rude to me.
I became a stepchild at the same age as DSD did, 11, and although my DSF (and mum) have their grumbles about each other, my mum and I always big up my DSF in our conversations. They're not an overly PDA couple but they respect and love each other and although I was a little shit at times in my earlier years, I never got the impression I could come between them or diss DSF. My DH also was raised by his mum and DSF from a much earlier age and it was v rocky and DH has admitted his over protective attitude towards DSD is due to not wanting to repeat that cycle, but it really hasn't served her well.
So I've come here for support just a handful of times over the last few years, posting as positively and child centred as possible, and although I've not received aggression, there's been a polite sense of, so what?