Null is disagreeance, neutral, and/or undecided. Some polls have both when it’s more relevant, but with official servers if there is not a paywall then it’s not relevant to the post (which is about revenue).
If a poll option was added, it’d be “I don’t support having official servers”, which is more likely to confuse people, but is basically “there are no official servers without some sort of paywall”. They may come eventually, for free, but at that point it is not relevant to the original topic.
The topic you linked already covers that opinion and harbors discussion around it, but the aspects of official servers it covers isn’t relevant to what this topic is doing.
The story is a substantial-ish part of U3, and is planned to be a more thought-out thing in U4.
Part of it is just that people don’t have much of a reference point, so everyone has to come up with their own. I added some images so people are a bit closer to the same page as to what they could expect, but polls can only do so much. It doesn’t cover all feedback, nor is it meant to.
Some people can just be opposed against one part of a much larger idea, but if they feel strongly enough about that one thing then it might not matter in the polls.
Typically, you collect a set and craft them together for a game badge. Crafting badges gives EXP towards leveling your Steam account.