First of all, Mumsnet is not solely a parenting website. Glad we got that out of the way.
Secondly, you're making plenty of assumptions yourself. I don't glare, tut or make comments when babies cry because I recognise it's what they do. It's rude and unhelpful when people do that. But I am entitled to think what I like of parents who could do something to minimise stress on a crying baby and be considerate of other people in the vicinity, and they simply can't be arsed to do it because they don't want their spag bol to go cold. It is naive and unreasonable to expect a wholly sympathetic response to a crying baby in a predominantly adult environment. Your waiting room example isn't the same thing at all.
No, I can't 'assume' that a crying child means they're tired. But sometimes - often - it does. And if you're lugging your baby round restaurants in the evening it's fairly likely that crying might sometimes indicate tiredness. I'd be sceptical if you claimed that had never happened.
Your right to take your baby to a restaurant does not trump the rights of other people to have a peaceful evening out. It's a 'PUBLIC' space for them too, and their comfort also matters. How do you know they haven't come out, potentially having paid for childcare, for the express purpose of having a break from their own kids, which then gets shattered because other parents can't be arsed to arrange childcare?
But anyway, as you're so completely closed to anyone's opinion except your own, and uninterested in reasoned debate, I'm out. Enjoy your day.