First off, you haven't defined "ignorant". You can't, either, since ignorance is relative, and is often used subjectively.

Then, the people in this subreddit will discuss if the comment is ignorant or not, and debate the arguments about this

So comments can be deleted if the majority of people on a specific subreddit disagree with it?

What gives this "internet police" subreddit the authority to pass judgement over someone else's opinions? Who selects/elects them? What rules do they use for their judgments?

These aren't just logistic questions, they are the purpose of democracy, free speech, and all the checks and balances that define western government. The point is that you can't create a system with power without creating a risk of abuse, so it's better to create as little power as possible, and severely limit what you do create. Hence placing branches of government (executive, legislative, judicial) in opposition to each other. It causes gridlock, but it's better than the alternative (see Russia, China, etc).

its just a story we've made up to convince ourselves that its ok for anyone to say anything and justify the idea that everyones opinion is equally valid

Free speech isn't about saying anything, although it does allow anything short of incitement, as it should. It exists because we can't be sure that the majority isn't wrong, so the majority shouldn't get to police the minority's opinions.

IRL, courts should adopt the "absolute free speech" position because you don't want the government choosing winners/losers in public forums.

But on the reddit, it makes no sense to let anyone say anything without consequence.

You say you understand the importance of free speech as a safeguard, but then you want to restrict it on reddit for some pretty bad reasons.

It discourages others from posting

So? If someone doesn't want to see disagreement then they can post in a subreddit that will produce a positive circlejerk instead, or make their own. No one has the right to not be offended. If you're offended by what someone (or a bunch of people) are saying, you can try debating them or just ignore them, or talk to your friends about how ignorant those people are and how you're superior and start whatever circlejerk you want.

If you want to shut those people up, all you are doing is showing that you are ignorant. You are so sure of yourself that you want to kill other opinions, because they are different from yours and so cannot possibly be right. But you don't get that power. No one does, and if someone does then all is lost.

Power corrupts, and the sort of people who will volunteer to be "internet police" are probably already pretty corrupt. Giving people power over others is a bad thing, and although sometimes it is a necessary evil it should be avoided whenever possible.

Also, one more thing:

debate the comments ignorance outside of the main discussion

Context is important.