Counter-Arguments Serve To Validate Your Piece
Though counter-arguments are not always required in college essays, adding them often leads to better results, as it shows diligence and a willingness to consider other facets of the subject. In professional pieces, you may want to consider adding them in every time, to preempt lingering questions in your readers' minds.
Good counter-arguments offer a reasonable disagreement with the main idea you are pushing, which you'll then resolve within the body of the piece. The result is an opinion that gets attacked, yet is able to keep itself intact.
Conceding Then Refuting
Rather than just presenting possible objections and leaving it at that, you'll have to find a way to show that your stance offers better value in spite of them. If you don't, you'll leave your argument thin and largely devoid of impact.
An effective technique for presenting counter-arguments is to concede to its validity (as in, there is good reason for people to adopt it) and then to summarily refute it afterwards (as in, it's not the best option). Done this way, you substantiate potential objections (as opposed to dismissing them) but also show how things can be handled in a better way.