Fascinating question. Off hand, it does seem that, in some cases, the motives you cite would make a difference. Imagine two people steal a sign advertising a bank that is involved with the unfair foreclosure of homes, leaving (let us imagine) many innocent persons homeless. A person who does the stealing as an act of protest and who, let us imagine, turns herself in to draw attention to this act of disobedience, seems (to use your terms) "less immoral" than one who steals the advertisement as a joke (perhaps using the sign as a tray to serve beer to friends while watching the world cup). In fact, we may find the person who did the theft out of matters of conscience heroic.
The difficulty in weighing motives, however, emerges when we dig deeper into why the persons have the motives they do. Is the person who acts to protest capitalism doing *that* solely for the sake of amusement? I came of age in the early 1970s and was present protesting the inauguration of President Nixon. A good number of us were protesting (or speaking for myself, I was protesting) as part of a date weekend. I did oppose the Nixon administration, but I also wanted to spend time with Melissa. Professing some overt political motive may not be the whole story. Moreover, there might be at least three factors that come into play in addition to matters of motive, and these involve (A) what is stolen, (B) how it is stolen, and (C) what happens after the theft.
(A) Stealing some things might be so gravely wrong that it does not matter what the person's intention might be. If I were knowingly to steal medicine that an innocent child needs and she dies for lack of the medicine, I think I should be judged equally guilty of homicide whether this was done to protest capitalism or for the sake of amusement.
(B) In terms of how a theft is committed, I think there would be a significant difference if the theft was committed violently or not, independent of motives. We might also want to factor in the mental state of the robber at the time: imagine the thief who was protesting capitalism was dangerously intoxicated or highly confused about the nature of property and capitalism. Similarly, imagine the thief who stole solely for amusement was under the confused impression that his amusing theft would help his friend coping with clinical depression. We might be more concerned about the thief's basic competence and mental health quite independent of motive. Silly examples, I agree, but they have some relevance.
(C) Our judgement on theft might be partly determined by what the thief does afterwards. Was what was stolen returned undamaged? What if the person who did the stealing out of amusement decided to use what was stolen later to help out the homeless?
Anyway, great question.