Well, let's hope he wasn't wearing the LGBTQ rainbow. In most Arab countries that would be a stoning offense. But hey, then he wouldn't have to worry about the sniper.
And I have the stones to answer to answer your false dichotomy question. But first, I'll remind you of the old saying: "2 Wrongs don't make a right."
But in a warzone, which is what that Israel sniper is facing, there isn't a presumption of innocence. I've seen enough videos of Afghanistan, Pakistan, and elsewhere to know that 12-year old holding an AK-47 isn't some 'innocent' child. I've read the stories of the shoebox bombs set off by kids during the Vietnam war. Heck, I've seen the death and destruction wrought by 'innocent' children within our own inner cities. And (as you've commented), its not like the sniper is going down and checking IDs before he shoots. A 15 year-old holding a molotov cocktail looks just an 18 year old. So while I don't condone murder, I do condone the protecting of one's squad mates in a warzone.
As for the on campus idiocy, what's gained? These Iphone warriors don't even know what they are asking for. They want their schools to divest from Israel. What does that actually mean? No more scholarships for Jewish folk? Not buy products from companies that sell to Israel? You know like Apple, Dell or Samsung? And unlike the Sniper, whose actions are directly against his opponents, the students (and outside agitators) are committing violence against whom? They are protesting against people who have no say or influence into the situation. The president of Brown or Columbia has no influence of the actions of Netanyahu or the IDF. Their actions on campus serves zero purpose other than to say "Look at me, because I'm a self-obsessed narcissist, who only knows how to whine and complain and have no capability of being constructive."
In the end, the sniper is doing his/her job. Its not an easy job. And its a weighty job. But that's the job. The protestor (in your example) is just being a whiny bitch. So I choose A.