There's no problem with adopting Marxist ideas into policy in the US. But a typical rhetorical tactic of the Republican party in the last 4-6 years has been to conflate liberalism with socialism. So now all liberals are considered socialists. The taboo with communism is essentially reversed: now it's taboo to call people communists because it was a popular propaganda mechanism in the last century. The new equivalent of that is socialism (though the repercussion are not nearly as intense this time around).
Socialism is strictly anti-capitalism, while liberalism can be (and in the US, generally is) pro-capitalism. In fact, liberal policies during FDR's presidency were considered to have saved capitalism. There is such thing as a liberal socialist, but there is also such thing as a liberal capitalist. That is, we're talking about two independent axes here.
a wiki intro to liberalism
Particularly, socialism literally requires redistribution of property as a fundamental premise; liberalism does not. Liberalism is about making changes to the system via policy. If your goal with those policies is to redistribute wealth, then you are socialist liberal (i.e. Obama and the Democratic party practice this moderately, but calling someone "socialist" is still distinct from saying they adopt social policies... still somewhat weasel language). But if your policies simply go towards more fair business practices or seek to curtail corruption, or to ensure that social equality is being enforced, then socialism doesn't play a role.
Furthermore, liberalism can lead to policies that redistribute wealth without being socialist because of inherit ideology ingrained in socialism (a sort of categorical imperative), vs. the emergent ideology of liberalism (the ends justify the means; i.e. if redistribution does actually make capitalism stronger, then redistribute.)
The Harvard Political review comments on this:
http://hpronline.org/united-states/liberalism-versus-socialism/
But basically, the problem is that as a result of this rhetoric, people think tend to think that liberalism is "at the expense of capitalism" when it is, in fact, a necessary part of it. Without updating our regulation and social policies to change with the times, we would eventually have anarchy, not capitalism.