I feel like the more people say "oh, this thread is going to get nasty" the more probable that statement is, like you are almost egging the nastiness on. If we come into it assuming that everyone is going to give their just opinions and be civil, then we are more inclined to respond as such.
No, I would not let my 1 year old eat McDonalds. And when she is older, I will explain to her why. I could just as easily make her her own chicken nuggets/burger/fries from locally grown organic seasonal food.
Now, say she is attending a birthday party at McDonalds (do they do that anymore? I remember one once when I was very young), she would be allowed to partake in the food as it is a special occasion, and I would not deny her that.
Knowing what I know about the way in which the animals are treated, the way the food is processed and stored and put together, I really just couldn't justify even giving it to her "in moderation."
Say we are on a road trip and it would be so easy to stop at McDonalds for a quick bite, I would instead find a local supermarket (if there's a McDonalds, there's gotta be a super market nearby) and find something that is already cooked and a lot more nutritious. If there seriously was not a super market, then and only then would I concede to choosing something from McDonalds to tide her over until we could find more nutritious food.
McDonalds has been a guilty pleasure for me in the past. I was given it not just in moderation, but probably once a week for a meal. I was often constipated and have struggled with weight and binge eating and seeking out delicious fried foods for a looong tiiiime. For the past couple years though, every time I've eaten it my insides have protested greatly, making for some pretty grim bathroom sessions.
I've struggled with crap food my whole life because my parents didn't know what they were letting me eat. I really don't want this to happen to my LO, I will teach her about good foods, and how different foods affect our bodies, and hopefully when she is old enough she'll be able to make her own informed descisions.