@Raevsky
This sounds like the sort of supportive group for dads as well as mums that I would've loved to have when I started out dadding. There are a lot of groups out there that are billed as being for parents, but in practice if you turn up as the only bloke you're generally unwelcome.
Well this particular one was advertised as being for Mums and Mums-to-be so clearly not for Dads... If you turn up to a Mums and Mums-to-be group, then of course you'd be unwelcome.
Parenting groups, which are mixed, do exist!
As the primary carer for my kids I've not found dads' groups particularly helpful. They are few and far between (there are none active in my city at the moment) and overwhelmingly attract part-timers doing their one day a week. You're never going to have a discussion there about which is the best local brownie group to send your DD to.
Why do women need to solve this for you? It isn't a women's problem if the Dads are shite at being helpful.
Also, plenty of Mums work part time (including ones who go to Mums meet ups), why have you dismissed part-time Dads?
And again, you could also seek out parenting groups.
It's seems nuts to me how many people on this thread are arguing for meet-ups and support for parents to be segregated on the basis of sex. Every uni or works social, every sports club or society I've been to in my life has been mixed, so the expectation that you should divide on traditional gender lines after having kids has felt pretty jarring (especially since my SAHD status puts me on the wrong side of that divide!).
Women's only sports, networking and friendship groups also exist! The fact that you haven't come across them or tried to gatecrash one is irrelevant.
Oh I'll pitch in in support of the guy turning up without the baby too. Perhaps he was going to take on more childcare when his DP went back to work and wanted to make some friends and contacts in advance of that. If I'd been in his position and heard of a parenting group that welcomed dads, I would've gone along too...
But this group was advertised as "Mums and Mums to be". You're coming across as yet another man who thinks that he's entitled to attend a women's only space.
In this context it just feel odd that now I'm doing a childcare and home making role that's overwhelmingly done by women, I'm expected to only spend time with other blokes.
Literally nobody has said you were expected to only spend time with other blokes. Why are you inventing problems where there are none.