Ask yourself, did you try to move your character during your first time through Helgen?
Did you try to see if you can walk somewhere or do something? Did you press W, A, S & D before the game told you about it?? Did you???
If so, and most players likely will have, it is what is called the survival instinct. You do not wish to be trapped, instead you want to be free!
For me did this very first experience svck, but I did not blame it on the Imperials. They caught me, I do not know how, but they must have been good. Or I must have been dumb or bad. Whichever. When they ran through the list and could not find my name on it, but still moved me to the block did I still note hate the Imperials. I only thought "Stupid soldier, does not get paid to think." ...
So I ran when I saw my chance, fetched the first loot, all of it (hehe), and saw to it that I get out. I was free. I started to figure out what got me into this and the dialogue suggested to have a face to face word with some Imperial. Good idea! Either I kill him or I join him. Turned out they know mercy...