Hacker News Reader

No, because the 'I think' does not mean what you think it means. You can't take it out of its social context, which is to inform people that you assign a lower certainty to the next thing you are going to say. (Of course, you could say all that, but that would make most conversations very pointless and annoying, as I can say from personal experience.)

You could say "I think the economy will be the most important issue in the next election", but you could also say "The economy will probably be the most important issue in the next election," which sounds clearer, as well as less refutable.

Clarity.

Because how are people supposed to know you are making a subjective/qualitative judgement? It's too easy to mislead people, and too many people profit from taking advantage of that.

A true argument can stand on its own.

They know by context. "Metallica is a great band" is obviously a subjective opinion and unprovable. It's the same as "I think Metallica is a great band" but with fewer useless words. This isn't misleading.

If I say something potentially provable that I am unsure of but claim is a fact ("Metallica is the best-selling band of all time"), this would be misleading, and I would be taking advantage of my audience.