Yet to do that he had to kill a-lot of people, namely the Jinchuuriki of the Tailed Beasts, people who deserved their own dream world to live a truly happy life more than most.

The principle behind his actions and plan were right. To give people their own dream world, a world where they live their happiest lives. But he practically took away free will to do so, and killed people to do so (again, namely the Jinchuuriki)

I think the One Piece Film: Red demonstrates being in a "dream world" where you are completely happy the best. Some of the people in Uta's world and wanted to stay there but some actually missed the actual world and the reality of going to school, being with friends, etc. It's fake. People will figure that out, we see this in the Shippuden anime with Tenten and once you do, some people won't enjoy it at all. Thinking about it myself, I would hate it. I won't ever get to see the people that I care about in reality which would suck that I can't actually enjoy my life in that regard. It's all fake. Forcing happiness that takes away the actual experience of life is the biggest problem.

I believe that the world Madara wanted to create is a utopia. Everyone forgets that the people inside the divine tree will turn into white Zetsu clones within +- 90 days. This calls into question Madara's dream of making the world a better place, rather it offers an alternative to living in an illusion for a while and dying. Also, it was Black Zetsu who implanted his dream into Madara with "Madara dream" sauce, further proving that Madara's intentions are a delusion. Madara was never right, he chose a false dream thinking it was his will. He was psychologically manipulated and he succumbed to it

It may not be entirely clear what I wrote, because I don't know English very well and have to use a translator, but you must understand the essence