Well put. Nothing wrong with idealistic visions so long as you dont confuse them with reality. You summarized my views well.
To recapitulate: true path to happiness lies in attainment of inner peace where you will not need to borrow from the external world in order to be content. Idealistic visions tend to encourage you to borrow from the external world because they suggest that you mold it into whatever you want it to be just so it can make you content in the end.
If you try to change the external world, it will corrupt you and you will lose touch with your inner benevolent motives. Bringing about external changes requires forcing conformity on others, this almost by property of itself must corrupt the inner being. This is why in history noone has succeeded in making this world heaven and only succeeded in making it hell.
Again, I can not stress this any more intensely...
I know of nothing better than to turn to within yourself in your quest for paradise because this world just isn't 'meant' for that.