I think even if it's true that these socialist countries are breeding a happier mind state amongst their populations, it doesn't matter.
I say this because happiness, as a standard of goodness, cannot be universalised.
For instance, taking the general UPB, example, applying UPB;
If; Happiness equals virtue, then;
if punching Doug will make Bob happy, Bob must punch Doug in order to achieve Virtue, ergo;
Assault is moral.
And by extension, assuming this makes Doug unhappy;
Doug is immoral.
This is clearly an unsustainable contradiction ('that's a funny tautology!' - he though whilst typing).
Also, I don't hear a lot of socialists saying, "well, all those loggers in south america seem to be pretty happy, good on them" or, "Those that get private healthcare are way happier, this is definitely the way to go!" or, "The rich seem far happier with their income, therefore...". You could go on.
I mean a lot of socio paths get a kick out of abuse and terror, but so what. If we take happiness as a standard of morality or goodness then we're back to a subjectivist view of ethics, or "anything goes, as long as it's good for my interests or preference".
So whenever someone uses this argument that socialist countries are generally happier, I think it's a reasonable position to point out that happiness is not a universal standard for judging or justifying the morality or sustainability of any given situation.