As a moderator on a different SE site that sees similar discussions (Philosophy.SE), I'd like to add a different perspective on this, although the first answer covers the main points pretty well already.
This is a political discussion site, right?
No, this is Politics.SE. That means that this site is part of the StackExchange network and thus has to obey its principles and model, for which the ultimate source is this FAQ. The model includes that questions and answers should only state verifiable, ideally sourced facts, that misinformation is discouraged, and that discussion in general is not part of the main sites but should happen in chat. As per the (compared to the FAQ) much less voluminous help center, the following parts are essential to the StackExchange model:
Above all, be honest. If you see misinformation, vote it down. Add comments indicating what, specifically, is wrong. [from Expected behavior]
Misinformation is considered wrong and should not be a part of either questions or answers.
If you see a post where many comments should be deleted, especially if there's an ongoing discussion, there’s no need to flag each comment individually. Instead, flag the post itself for moderator attention, choose the "in need of moderator intervention" reason, and explain what's going on. [from What if I see something bad]
Comments should not be used for discussions. As a matter of fact, there is a message template for "excessive discussion in comments" for moderators to choose when they contact a user to make them aware of problematic behavior. Continuing with that behavior is a potential reason for suspension of the account. If you want to add a comment, the box always says "Use comments to ask for more information or suggest improvements". That is meant as a rule, not a kind suggestion. For more on comments, see this Meta.SE post. The fact that the mods here tend to be lenient regarding comments (as am I on Philosophy) does not change the fact that comments that do not meet these criteria can be deleted at any time simply for that reason alone.
Who decides what is misinformation or not? Just the moderators?
Ideally, moderators should not have to decide on such cases much because high-rep users can cover much of the moderation duties by themselves. Smaller sites are not ideal in that regard though, both because they tend to have fewer high-rep users in the first place and less of them being online at the same time. As you can see from the above, every user above 125 reputation can and should decide whether something is misinformation, simply by voting down if they think so. That is what StackExchange is about: the community as a whole decides all individual cases and, ultimately, even the rules themselves. Mods are nothing more that some trusted community members enforcing these rules to the best of their abilities. They have to decide more on smaller sites and believe me, they wouldn't if they had the choice.
How does it help to educate people? All it does is indicate that "the moderators think your answer is wrong so it has been deleted". Sure you can cite sources that state why the answer is wrong but wouldn't it be easier to understand why if you had the answer still present for reference on the Q page (without being moved to another edit history link)
This helpful post on Meta.SE states everything you need to know on who can delete for what reasons on answers specifically (since comments were covered above). Regarding reasons, it has the following to say:
For answers, any post that is not an answer (should be a comment, doesn't answer the question, etc.) should be deleted. Answers that are wrong or that dispense poor advice should be downvoted, not deleted.
Therefore, in general, misinformation (being wrong) as such is not a reason for deletion. Not answering the question as it stands (and offering an alternative narrative to that in the question instead) is, though. Also this is only part of the story, since the next paragraph says:
These are general guidelines; some communities in the network may uphold more specific reasons to delete posts or not. For example, on Puzzling.SE, answers to a puzzle without explanation are subject to deletion, and some technical sites will delete answers which are not only wrong but also harmful when tried.
Therefore, it could be argued that opinionated answers that do nothing more than giving a political view that is verifiably based on and promoting misinformation are harmful for a community that is supposed to be delivering facts on political matters. On the other hand, only the highest rep users can see answers with a score of -4 or lower, so downvotes and comments may still be preferable.
This does no mean that this could not be part of an answer at all. It should be clarified that this is the misinformation a given political party is promoting in an answer though.
Are all the good questions on this site all able to be answered objectively? If not, then misinformation becomes not the deletion of falsehoods but rather the deletion of opinions which other users find "ungood"
Short answer: Yes. Long answer: Yes, questions on SE should be answerable "objectively" in the sense that there should be reliable, reputable, external sources that can be used to base an answer on. Every question that soliticts opinions should not be answered and downvoted instead:
Some subjective questions are allowed, but “subjective” does not mean “anything goes”. All subjective questions are expected to be constructive. What does that mean? Constructive subjective questions:
• inspire answers that explain “why” and “how”
• tend to have long, not short, answers
• have a constructive, fair, and impartial tone
• invite sharing experiences over opinions
• insist that opinion be backed up with facts and references
• are more than just mindless social fun
What is the principle behind misinformation anyway? John Stuart Mill did write "If all mankind minus one, were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind."
Now this is borderline trolling and I think you know that. SE is a private company that provides a vast framework in terms of software, hardware, and personnel, not a state. It is perfectly within their rights to determine limits of behaviour for the users of these sites. As a matter of fact, you agreed with these rules when you registered your account.