People that would side with the Stormcloaks based solely on that single Imperial Captain are choosing them for foolish reasons. That's like choosing a political party based on the actions of a single person, you have no real idea of all the extraneous aspects you embrace by doing so.
If you feel the need to follow Ralof for the pleasure of slaying that corrupt Captain, by all means do so. But to not even give the other Imperials (for the most part, honorable individuals) a chance is a decision based on pure emotion and hatred, not reason.
No it is not a foolish reason at all.
They tried to kill you! They wanted to chop of your head. I didn't see anyone else saying 'hang on a minute... that person wasn't with the Stormclaoks, they aren't on the list, should we reconsider this... maybe just hold them for questioning'
No You don't get squat all help from the others, just a demonstration of why running for it is not a good idea. it isn't 'just' a corrupt Captain, it's the whole lot of them standing by watching. You are not even worth considering for a repreeve or second look - but hey it's just paper work so thats ok....
How am I suppose to sympathise with a bunch like that? Why should I be enthused about joining them?
My first thought would be 'if they find out I was going to be neck trimmed at Helgen, then maybe they will want to finish the job off'. I can see so many reasons to avoid them.
'O well, it was all a jolly good laugh - sorry about all that head on the chopping block axe swing down stuff. no harm done eh' Sorry that doesn't cut the mustard.
So to me they are facing an uphill struggle for my support from the outset.
The Stormcloaks are neutral at that point - nothing to go on, but at least they didn't just try to kill you. yeah they turn out to be arses, but not much more so than the Imperials really.
For someone who has travelled and knows the true face of both sides, it is a fair choice, but how can you even consider running to join the Imperial faction at game start after waht they did?