As Sychov himself explained, his motivation to stay with the Ukrainian soldiers was the realization that the Russian command had given orders not to take prisoners.
He understood that Russian troops could kill him along with the Ukrainian defenders.
He didn't join the Ukrainians out of some deep conviction that the war is wrong, he just didn't want to get murked by his own people.
Yes I'm sure Harris would have been terrible, a real boot to the neck indeed. Better to have Trump instead