If you read the OECD reports on inequality, you'll see that it stifles economic growth. That's an indisputable fact now.
No it is NOT a fact. It is opinion on causality inferred from a correlation analysis. You really need to learn what a fact is. A fact is they found a correlation. The assertion that one caused the other is an opinion. I have seen this BS in paper after paper where scientists keen to push whatever hobby horse they are flogging ignore such questions because they are inconvenient.