But what I will say is this (even if it's a bit utilitarian without paying enough respect to other theories): The person who fills in for you is probably being harmed less than the person who sticks around. The guy who backlogs for you? He shrugs, maybe cusses "**** a losing WZ!", and then just leaves the game; because he joined the game late anyway, he feels no agency in its loss and no investment in its outcome. So he will just requeue having wasted very little time and experiencing very little frustration. Or maybe he loves the uphill fight so he stays around to play it out! In that case, you did him a favor.
For you, however, by remaining in the WZ and wasting your own time on a thoroughly unenjoyable activity, you incur a big hit to your own happiness. Your own loss of happiness, not to mention 10 minutes of your time, is comparatively much larger than the minor frustration and wasted 60 seconds experienced by the backlogger.
It's not the ONLY way to view the ethical problem, but it is definitely one way to do so.
I think your position on the matter is more narcissistic than utilitarian, but I absolutely love that you brought I. Kant take-it-anymore into a swtor pvp debate. so cheers!