You very much do have the right to do that, as you should. And you don’t have to justify it for any reason.
But IF you have a preference between the R and D candidates, and somebody points out that you mathematically helped the one you dislike by voting third party or staying home, they are still correct. It’s not any kind of moral or ethical thing on its own; it’s just a side effect of how our voting system is designed.
I meant that pointing out that you’re helping the person you don’t like isn’t a judgment call or an insult or anything. It’s just describing the mechanics of the system, whether you prefer the good guy or the bad guy.
Your actual vote choice is chock full of morals and ethics though!