Collectivism trends towards totalitarianism. Many ideologies that would fall under socialism do tend to be collectivist (though there are a couple exceptions). Once you start viewing the group as the basic unit of society rather than the individual, you value some sort of ultimate utility (or utilities) rather than subjective value. This removes the purpose of freedom of association and rights when ever they conflict with the ultimate utility. You can justify any action as long as you believe it will increase your ultimate utility, namely authoritarian policies. This doesn't apply to just socialism however. Other ideological areas this trend applies to include traditionalism and populism.