The question could have answers that are not opinion-based.
I can think of two ways that this question can be answered that are not opinion-based.
- The makers of the films let it be known that the name was chosen for some particular reason. So far, nobody has found such an answer, but that doesn't mean that one won't be found.
- Someone can explain the meaning of the name. If someone answered that "Sidious" was an old term for "X", that would be an answer that was not opinion-based.
So far, there haven't been any answers that meet either of those criteria, but that doesn't mean that there couldn't be one, so I don't consider the question to be "Primarily opinion-based".
Most of the existing answers are along the lines of "Sidious" makes English speakers think of "insidious". That seems like a very reasonable opinion, but not a definitive answer. You could comment on the answer to say that it lacks verification, and you might choose to down-vote it for the same reason. But those are not reasons for closing the question.
Questions are usually closed based on the flagging and close-voting of regular users. Moderators would, and should, only circumvent that process in exceptional cases.