Reporting valid issues does not grant you the right to abuse the issue tracker.

I'm not saying it does. I'm saying that banning a user who is making a mistake in one area means you lose the value they provide in another (which might be valid issues, but equally it might be 90% of your revenue or something), so it's not always an obvious decision to just wield the ban hammer every time. Moving discussion of issues before they're created to a separate place helps keep the issue tracker focused on issues that are likely to be addressed.

An additional benefit of that is that a user whose discussion leads to a real issue being created will feel like they're genuinely being listened to. That creates a good customer experience, which is good for your brand's reputation. It's a positive experience. Closing non-issues in the tracker is a negative experience.