Honestly I'm not super invested in whether the argument is "correct" or not, I'm invested in the actual situation that affects actual people's lives. I personally don't make my decisions on what opinions to espouse and who to try to convince of anything based on a rigid structure of "validity" of an argument. It helps and it's a decent indicator of the right way to go sometimes, but if I know something is going to have a negative effect on people's lives based on whether or not I spread the idea or opinion, I don't care if it is "valid"/"correct" or whatever, I care about the
effect. It is also important to note that even if the argument is not correct, that does not mean that the conclusion is not. A fool with no notion of "proper" argumentation can make an argument espousing any conclusion (right or wrong) that comes to him, but that has no bearing on whether any of those conclusions were right or wrong (also known as the fallacy fallacy)
I have this concept I use internally a lot where I consider what I believe to be true and what I consider to be "useful", and sometimes I will choose to believe things that I am sure are false because it is more useful to me personally to believe it is true. One example of this is the concept of karma. I am don't believe there's some mystical force in the universe that will balance everything out and ensure "what goes around comes around", but it sure is useful to believe in some mystical balancing force so that I don't feel compelled to avenge every instance of me being wronged. Instead I just let it go and assume that the universe will right itself. The previous paragraph is taking this type of analysis to an external level when I decide what I will propagate with my time and energy and what I will simply read and move on.
I don't particularly care whether or not the idea is structurally sound for some framework of debate and a system of rules for determining if it is valid or not, I'm more concerned with the real implications of believing and propagating belief in the idea. You mention that it's not the same net effect because personally deciding not to vote would change the tally by 1, but the voter suppression targets a group of more than 1. Yet here you are trying to spread the idea to other people to convince them that they also should join you in evaluating this idea as correct and thus not vote. This increases that count to more than 1, and the better you are at it, it increases further. It is exactly the same net effect because humans are social creatures and ideas spread through socialization and group acceptance. People who read your post and agree with it will feel that your reasoning justifies their belief in not voting as well. In a way, whether intentional or not, you are commenting on this topic in a way that serves to disenfranchise voters through self-disenfranchisement. If that is not your intent, I would ask that you examine what the effects of your efforts are and how they align with your goals in life and reality and perhaps focus less on systems of logic that are meant to help simplify and parse arguments, not determine your every action.