I think you took a karma hit not for saying unpopular things, but for assuming bad faith. One of the lead developers of the Rust language pointed out some gaps or mistakes in your comment about Rust. Instead of appearing eager to correct yourself, you appeared eager to defend your original statements and all but accused him of lying. I'm certain you could have made the same substantive points with a more reasonable/humble tone and not been downvoted.
For example, when you learn new information like "there's a tracing GC in progress" and you want to look at the source code, you could choose to say "Oh, cool! I didn't know that. Could you give a link with more information or source?" instead of lecturing the other commenter about how they are Doing Open Source Wrong.
I don't have a position to defend, and I am nobody to make any statements of any significance: I did a code review, and I was critical about it. If anything, I want the project to succeed. Evidence? [1]
He asked me why I thought Rust would've live for long, and I spent hours reading the code and writing a detailed coherent comment to the best of my ability. He dismisses my comment as "FUD" [2] and responds with one-liners. The final comment with a link to his blog with colorful graphs was terribly condescending. Him being a lead developer doesn't mean squat to me: a bad argument from him is still a bad argument.
No, I'm not going to stoop to begging for scraps: if I wanted to do that, I'd be using proprietary software; Apple or Microsoft nonsense. In this world, the maintainer is the one who has to take the effort to educate potential contributors. He is clearly doing a terrible job, and I pointed that out.
No, I never accused him of lying. I accused him of making a bad argument, and not giving me sufficient information to post a counter-argument, which is exactly what he did.
And no, I did not "defend" my original argument: I posted a fresh review of fresh code (the one in src/libstd/rt, as opposed to the one in src/rt).
On the point of tone. Yes, I've spent many years on harsh mailing lists and my language is a product of that experience. Are you going to discriminate against me because of that, irrespective of the strength of the argument?
I will repeat this once more: the only currency in a rational argument is the strength of your argument; don't play the authority card.
For example, when you learn new information like "there's a tracing GC in progress" and you want to look at the source code, you could choose to say "Oh, cool! I didn't know that. Could you give a link with more information or source?" instead of lecturing the other commenter about how they are Doing Open Source Wrong.