I think it is partly the want of independance, like in the example about holding hands. For us there are places they don't have to hold hands when walking, but if crowded it is not an option, and if they pull away I hold even tighter. For my younger one I would just pick hjim up and carry him, which he doesn't want, so he gts the choice of carry or hold hands.
Sometimes I think the rudeness in little kids is from not having the vocabulary or the skill to know how to get your point across in a polite way. When you think about english and how things are phrased, things are not said directly, especially neagtive things. Little kids say things directly, they just don't have that skill yet. So they will say "don't sit there, thats may chair" instead of, "Excuse me please, I was sitting in that chair". When my kids say something rude I make them repeat the sentance in a polite manner. At first I have to tell them what to say, but after repeating it over and over and over they get it. My 5 year old can rephrase his own words politely now when he is rude, but my three year old I have to remind him what to say.