Your primary options are to downvote or to leave a comment suggesting improvements to the answer; I can see that you have done at least the latter, which is a good start. You can also flag as "not an answer," but bear in mind that typically, this flag is only upheld when an answer egregiously fails to address the question and talks about another topic altogether—for instance, if someone posted a link to their Avatar: The Last Airbender fan-fiction that they thought was relevant to the question, or posted another question instead of an answer.
That said, in this particular case, it might be good to consider that many of the answers might not be as irrelevant as they seem. From my perspective, the ones that you mention supplement your answer.
The one answer mentions that many student protesters have divestment from Israeli interests as a primary goal; your answer expands on that. That answer also points out that students may benefit from protesting at the institutions that they are studying at in terms of sympathy and convenience of organizing the protests. One might disagree with these assertions, but they are not irrelevant.
The other answer, even though it does come from a user that has exhibited a bit of a bias toward supporting the Israeli government's actions over Palestinian rights, nonetheless is relevant because it asserts that the campus environment is more convenient for protests than places like the United Nations building. Again, one might disagree, but this is at least a relevant argument.