Okay, so there has been plenty of analysis on what exactly defines chivalry, and what his motives were like, but perhaps you guys are being too specific. Because the details are so sketchy, it's a logical fallacy to pass judgements on events that MAY or MAY NOT have taken place. For any mathematician, statistician or scientist, uncertainty in a solution can only be clarified to the least accurate piece of data in the original problem.
So, the first thing that needs to be clarified is this: Are we talking Robin Hood specifically, or are we using his usual stereotype identity as an example to represent the Chaotic-Good archetype?
Historical figure
If we are talking about the actual guy, then only so much can be judged fairly, simply because the records are lacking in depth and in backup. But rather than analyse the actual specific actions, perhaps it is better looked at this way: Hypothetically, when King Richard finally returned, would any of you have objected to the idea of Robin being knighted for his crusade and cause? I certainly wouldn't. IMO, whilst he may not be the stereotypical knight, his overall actions certainly warranted the level of respect and recognition granted to the more usual form of knight. That being said, he was not knighted, so perhaps that, in itself, is evidence that the more shady business was more evident than the tales describe, enough so for King Richard to think it inappropriate to knight him.
Archetype
If we are using the usual, romanticised version of the character to represent the Chaotic-Good archetype, then it really comes down to the style and situation of his rebellion.
If he is rebelling against a Lawful-Good government, where his only real problem is the idea of a lack of freedom, then perhaps he is not such a good character.
If he is rebelling against a Lawful-Evil government, (which is what the tale usually depicts it as) where he has both a problem with the manner and the oppression, then perhaps he is a good character.
If he is rebelling against a Chaotic-Evil government, where he disagrees with the ethics and morals of the other-wise socially driven system, then perhaps his intentions are still pure.
If he is rebelling against a Chaotic-Good government, then it really is just a civil war, where two powerful forces are involved, and like repels like. In that case, it's very hard to pick who is on the right side without knowing the specifics of the politics involved.
The problem with chivalry, in this case, is that it is usually considered a fairly linear, uni-dimensional spectrum, whereas one's chaotic/lawful alignment may need be taken into account, depending on one's views ON chivalry. This would make it a two-dimensional spectrum, and a lot more complicated.
Now, I have been using chaotic/lawful and good/evil spectra, when in all fairness, it's all relative according to the politics involved, so perhaps the spectra would be better labelled as "Action" and "Intent" respectively.
Which boils the whole debate down to this. Is Chivalry based purely on one's actions, or purely on one's intent, or on a combination of the two?