Any socialist worthy of the name does in fact believe in humanity, it’s kinda the whole point.

Why do people associate socialism with authoritarianism? They are incompatible. Socialism should strive for egalitarian society which is one of the opposites of authoritarianism.

The USSR was supposed to be Communist but failed utterly. Then the wall fell and Russia became instead an authoritarian kleptocratic capitalist state. China is nominally Communist, but again if you want a “worker’s paradise” it’s probably worse than the USSR.

Of course, the problem is that socialism (like capitalism) is an unstable system and will collapse if left to its own devices. The Communists and Libertarians live in similar La La Lands, longing for something that can’t survive on its own. No matter what you do, some people will either want to be elite, think they are, or actually be, and they’ll exert a lot of energy to take over.

But the original point stands: if you want to appeal to common humanity, your only allies will be on the left. Maybe you should put more pressure on the people who need it the most(?)