Husband left his friends who I don’t know alone in our house with our 6 month old

No YANBU. They could have been anyone. Who knows whether they might have fed the baby the wrong thing, put them to sleep on a sofa, not noticed that a nappy needed changing. Would they have known what to do if the baby started screaming, was sick, or worse injured herself. I’m not even going down the road of child abuse or shaken babies here for it to be pretty bad.

He should have taken the baby to A&E with him, asked his sister to take a taxi or at worst called you and dropped baby at the brunch on his way (not ideal but I’d have preferred this to leaving her with three total strangers).

Well that's it, isn't it? A women has the ability and authority to judge the responsibleness of their friends, and a father would be judged as controlling for daring to question this, but the father doesn't have this ability or authority without consulting the mother.

Then, a few months/years down the line we'll get the AIBU of "My husband does a bit, but I carry the mental load, I make all the decisions, he can't do anything without asking me, I'm mentally exhausted, I need him to step up" and she'll get the usual useless man responses, LTB etc.

Why does it matter mum doesn't know them when Dad knows them well

Better than leaving the baby with people the mum doesn’t know.

Well that's it, isn't it? A women has the ability and authority to judge the responsibleness of their friends, and a father would be judged as controlling for daring to question this, but the father doesn't have this ability or authority without consulting the mother.

Then, a few months/years down the line we'll get the AIBU of "My husband does a bit, but I carry the mental load, I make all the decisions, he can't do anything without asking me, I'm mentally exhausted, I need him to step up" and she'll get the usual useless man responses, LTB etc.

Do you not understand the concept of friends?
When my child was young I often invited friends round when DH was out. It was easier than going out with a baby and meant I got to see my own friends too.
Parenting doesn’t have to be isolating and good friends are interested in getting to know your child.

If it was a woman posting that she invited friends out while her Husband was out for the afternoon nobody would bat an eyelid.

I also suspect if a women posted that she’d left her baby with a friend to deal with an emergency then the replies would be very different.

You hope they have. But six month olds are crap at talking aren’t they, so OP just has to hope the baby was perfectly safe. She couldn’t take a judgement call as she doesn’t know these people in question and her DH didn’t run it past her.

No he doesn’t drive a mini bus (that I know of)
However I commented before I seen that the a&e was a drop off and not waiting around with a baby.
I do think that it should have been discussed before leaving the baby with anyone else. Anything can happy at any time .
Tbh I think it’s poor that the dad needed his friend around to sit with his child for the first time alone .

No he doesn’t drive a mini bus (that I know of)
However I commented before I seen that the a&e was a drop off and not waiting around with a baby.
I do think that it should have been discussed before leaving the baby with anyone else. Anything can happy at any time .
Tbh I think it’s poor that the dad needed his friend around to sit with his child for the first time alone .

oh please. His car runs on free petrol?

but if that’s the case I can see why your husband felt that was an only option. If you scraped money for this brunch then it explains why he didn’t call you - he didn’t want to ruin your only treat by either having to leave early or worrying about the baby.

The baby evidently was perfectly safe. OP arrived home and the baby was fine.

Statistically it would be in more danger travelling in a car.

Some mothers actively cultivate the dynamic in which they are the expert parent, the one with all decision making powers through whom all decisions must be agreed and then complain when the father abdicates responsibility or treats her as the default parent once the child gets older. Don't be that mum. Your DH is equally her parent and these are people he trusts. She was fine.

You hope they have. But six month olds are crap at talking aren’t they, so OP just has to hope the baby was perfectly safe. She couldn’t take a judgement call as she doesn’t know these people in question and her DH didn’t run it past her.

Does he drive a minibus now?
Why shouldn’t he have left his child with his friends who he has known pretty much his entire life and obviously trusts?

Where did I say the injured child shouldn’t have been prioritised?

Why does he need reinforcements when you leave the house? And why does he need company, can he not be on his own?

Sorry I feel like I should clarify.

These friends of DHs, none have children of their own, but they are all from a more family oriented culture so probably have experience with nieces, nephews, cousins etc.
DH has known them since he was a toddler, he and his mum moved to the uk after his dad died and then a few years later his friends moved to London. I have met them but not super often and I wouldn’t say I really know them.

Frankly, better for her to be irrationally upset than an injured child not be given priority.

Why does he need reinforcements when you leave the house? And why does he need company, can he not be on his own?

Well it clearly upset her that’s why