I don't think anyone has been hysterical about this, everyone has said in moderation it's fine for an older child, just surprised that the thread seemed be saying it was normal for a baby to have its own happy meal. It's not, is it? I don't think it's over the top to be a bit particular about what your young baby eats.
People saying a lick of chip or nugget is fine, and MacDonalds do serve veg - the op said eating nuggets and fries, so that's neither here nor there! My baby could polish off nuggets and chips no problem, she wouldn't stop at a lick.
My ds isn't restricted anything in terms of food now and has something like this every few months, he quite enjoys it, not a big deal, not a massive treat, just food on the go. He used to get carrots and still gets milk with it. He doesn't feel deprived, never asks to go there.
My niece, who went once every week or so from when she was around 9 months (I didn't start a thread about it) bangs on about it all the time and only ever goes for heavily salted, processed options when she's out. She is slim, but doesn't eat healthily. So it works both ways, it's not limiting this stuff that makes them crave it IMO, unless perhaps taken to the extreme of it being forbidden fruit.
At 9 months they would have no notion of the concept so I was strict, it's easy to not give them this when they are babies and not set them up for problems in later life.
Agree with Mintyy, you can't judge a baby's healthiness by its slimness. My 8 month old is is 12-18 month clothes, that's largely milk and vegetables!