Consider...

• A "downvote" will move a vote farther down the page, (an upvote, vice versa).
• According to the instructors of this Udemy course, internal social media research found that posts are more likely to get more engagement the higher up they appear in lists.

So... A post is new, it has one other "zero-rated" answer, post an answer yourself, vote down another answer, you get prime real estate... That smells like a conflict of interest.

It wouldn't fly for an athlete to sit on a judges' panel while also playing in the same game. Should that principle apply here?

I'm sure there are algorithms and system checks on people who do this. But, frankly it shouldn't be allowed at all, unless there is a good reason, which I would sincerely invite (honestly).

Ideally, all voting "should" be disabled when answering, including up/down-voting on the OP itself. But, the world isn't perfect, I respect that there may be lots of snags with that, and it might be under discussion already.

I'm just a new guy looking for wisdom from the high-reps. Teach me and teach us all...

Should voting—on other answers or on the question itself or at least down-voting—be disabled or automatically retracted on a question that a user answers?

It would solve this issue: If you just witnessed tactical downvoting, is it a reportable offense?

And addresses in more detail this: The answer to tactical downvoting problem?