Why is it that criticism of people's insatiable greed for wealth and power often gets dismissed with this thought-terminating cliche about utopias?
Desire to live in a society that's less greedy, that rewards compassion and punishes sociopathy is completely valid. We should be pursuing that earnestly because survival of our species depends on it. The people in charge are so drunk on wealth and power that they would rather drive our entire species off a cliff than sacrifice even 10% of their effectively bottomless wealth.
But instead of criticizing our current philosophy that's actively being taken too far and threatens to destroy us, you criticize people who express their frustration with this state of affairs.
The criticism is not of the idea that the world has problems, and that we should look at those problems with the aim of fixing them.
The criticism is of the assumption that a world without problems theoretically could exist.
You may disagree, but you will not find a definition of such a world that everyone can agree on.
Regardless, of whether you agree (that such a definition doesn't exist) or not, if you do plan on bringing about such a utopia, and you begin to meet resistance, the question you will inevitably need to answer is: How do those who resist fit into this utopia?
The historical answer for this question, which by all appearances seems like an inevitable answer, is the reason why people criticise utopian thinking.