Instead of what - what they do, presently, and have for decades?
There's one thing worldwide Communism opposes, and so modern day western leftism as well - and Fulton Sheen wrote about it - religion, and specifically Catholicism (though its been weakened under the two PC Popes). For all their changing rhetoric, and 'plans', and 'third ways', and what have you, the Commies are consistently, militantly atheistic or pagan, and opposed to Christianity. The latter is the 'rulebook' for life, the statement of the one great choice we all make in this life, our purpose in being here, and the structure for a just and civil society, and so on. The former is a manmade substitute, bound to tyranny and oppression, injustice posing as 'justice', political correctness, liberalism in most all forms, and the future which is opposed by most on FR and all reasonable people of Faith.
There are plenty of religious people who are communists. For an example look at any Israeli kvutzah or kibuttez. The nature of its collective-ownership and raising of children by the community is far beyond simple sharring of resources at a nunnery.
http://en.wikipedia.org/wiki/Religious_communism
The difference between our system and a typical communist government from 20th century is that, the communist government will nip "deviants" in the bud, while we tolerate all kinds of hippies as long as they don't become a major problem. If a group of religious folks want to form a commune, they're free to do so as long as they can afford it and don't break laws. But if a majority of Americans want to adopt Amish lifestyle tomorrow and cause a huge drop in tax revenue, I think the government will step in and do something about it, like requiring their kids to attend high school.