I’d call it a draw due to each considering the problem in different "social" reference frames.
Unclenick is correct from the standpoint of considering statistical probability over the time frame of the course being offered, but a statistical standpoint of considering each class as a separate frame would change things in favor of Jammer Six’s position.
However, Each standpoint can only reach a moral conclusion by defining fairness in relation to their chosen frame and equating it to moral justification. This is a subjective judgment. Therefore, neither "truth" can be defined as objective. Allowing both to be considered "true", or choosing one over the other, leads to situational ethics, imo.
An easy way to resolve the two is to dispense with the notion of fairness, and allow each of the participants to choose the level of protection they desire, bounded by their ability to acquire it. It then becomes morally wrong for any participant to forbid or require anyone else to wear a vest. (this excludes integration of private property rights and other mutual agreements on conditions … just for simplicity’s sake
It also dispenses with the notion of truth as an application to a situation. Truth is only defined as a formula for correct operation. Variables in the formula exist to describe various situations. So …. Resultants are applications of the formula created by substitutions of variables, and nothing more.
And each person’s "correct" perception of truth can be different, while preserving the notion of objective truth. The Devil is in the details, and God is in the formula, so to speak.
Long story short, If you want to wear it and can … it’s perfectly ok to do so, a neutral act. If someone else wants to wear it and can’t, providing for them to do so … would be a good act.