Why both fascism and socialism lead to tyranny

Many socialists consider their ideals to be somewhat "just" or "fair", and that they have nothing in common with the terrors of Nazism of Fascism. But there is a strong resemblance. Hayek explains:

"Planning", therefore, is wanted by all those who demand that "production for use" be subsituted for production for profit. But such planning is no less indispensable if the distribution of incomes is to be regulated in a way which to us appears to be the opposite of just. Whether we should wish that more of the good things of this world should go to some racial élite, the Nordic men, or the members of a party or an aristocracy, the methods which we shall have to employ are the same as those which could ensure an equalitarian distribution.

...says Hayek in his Road to Serfdom (pages 34-35 in this edition).