to be upset at a mum bringing her contagious child to an meeting to a

[mamaloco]

Here is the story: Yesterday, a coffee morning for infos, chat and charity sales. Some toddlers and babies, a few pregnant woman, may be 100 person with wide spread ages. More "me time" kind of thing that a "I have to be there" thing.
One little girl school age, no worries, untill somebody told "Oh you are the little one with chicken-pox".
It is very contagious, and you can't be sure that all the adults here had it, even less the baby.
It think mums who takes their contagious and unwell children to playgroup, party, meetings are plain selfish and don't think about the consequences of their action.
BTH I might be angrier because I caught chicken pox from someone's kid at a diner party because they couldn't find a babysitter. They didn't warn anybody beforehand . I was sick for a month with it had to be on antiviral, very weak, some of my friends even ended up in hospital with it. (all 25+)
I know it is hard to stay at home and you crave human adult contact (my DD was sick a lot for 2 years, so I cancel a lot of things because she was contagious, and I was going slighty insane). But it is unfair the the child who should be resting, and to the people who will catch the disease.
Surely you should contact all the people present first and ask if it OK, no?

perhaps it was her mum running the coffee morning and she had no childcare options ?

I don't think YABU. Not everyone is respectful enough to quarantine their dcs when ill, IMO. A friend brought her child with CP (spots only appeared the night before, child still had a fever, FFS) to ds's 1st birthday party. Which would be bad enough, but everyone had been warned that one of the guests was severely immunocompromised, and to let us know about any illnesses so he could avoid them

YANBU people don't think.
A lady at our bf group took her baby to groups etc even though she was unwell. No, she didn't know what was wrong with her DD - she had a rash, fever, refusing food etc
It turned out the baby had measles. Fair enough she didn't know, but she exposed loads of children, babies and pregnant mums to measles.
Heard a story once about a couple who took a child with CP to visit a child on the cancer ward honestly take an infectious child into a room full of kids whose immune systems are virtually non-existent due to chemotherapy. Clever.

I think that some parents are rather selfish. They don't want to be stuck inside/miss out so they decide to take a bit of a risk.

Thing is, the risk for them is that their own child might be sick/feel tired or become a bit more unwell.

For the people they are mixing with (who had no choice in the situation the op described)the consequences may be far more serious.

Yes, it may be unlikely that there is someone else in the group who is pg/unwell/receiving chemo or whatever, but that's not the point is it.