I can see where standing on a booth is rude. But staring at other diners (especially if you're NOT in a booth)- even if the toddler is twisted around- is kind of a given. My thoughts are it depends on what sort of restaurant you're in.
We regularly take Ducklet to a place that really caters to kids, although it's a "grownup" place in that they wait on you and you can actually get wine or beer. A lot of parents take kids there- it's a great place to begin teaching restaurant manners (especially since they're very accommodating about "to go"!). It's a local place, with a train running around the top border of the dining room. Naturally, Ducklet twists every which way to see the train, the people, whatever. I try to keep him from bothering other people, but if he's watching quietly... well, sorry. I can't help that.
I don't think kids should be allowed to rule the world, obviously. But there are places- and not just fast food- that people have to accept kids will be there. Places like Max & Erma's, Friendly's, Applebees... those sorts of family restaurants are "kid friendly." If a young child is acting up, that's not acceptable. But if a person really can't handle a two year old at the next table watching them quietly, they should either ask to have a different table or go to a place that's more adult oriented. People are fascinating to a toddler, and that's something you really can't change.
That said, I do think older children should be taught it's impolite to stare at other diners. But a very young child who simply doesn't have that sort of attention span needs to be granted some leeway!