EGALITARIANISM IS NOT UTOPIA!
Egalitarianism is NOT a utopia; it is not a perfect society in which all problems have disappeared. It is, however, a whole lot better than any society based on class inequality, such as our present one.
First of all, egalitarianism is NOT based on the premise that ALL people want an egalitarian society. It is based on the premise that most people do, and that the majority can prevail over (by force, if necessary!) the minority who oppose egalitarian values to make society be shaped by the egalitarian values of the majority: equality (no rich and no poor) and mutual aid.
In an egalitarian society people with egalitarian values have gained the upper hand and have the real power in society, but this doesn't mean they are perfect people. There will still be problems stemming from the fact that people are not saints. There will still be individuals sometimes doing nasty things to other people. Selfishness will not disappear.
The difference is this. In a society based on class inequality there is official approval for some people to have extreme power to dominate others and to act in extreme opposition to the Golden Rule. In contrast, an egalitarian society is based on principles that promote rather than impede egalitarians' ability to oppose any individual or group of people attempting to gain the power to dominate and oppress others or act in flagrant opposition to the Golden Rule.
It's not utopia. But egalitarianism is much better, and worth fighting for.