"Socialism and capitalism can't exist together..."
(Except, of course, when they do. Which, up to now, has traditionally been the case.)
You can argue that it's not a PURE system, but that's an ideological, not historical, argument.
Saying oil & water don't mix doesn't mean they can't be made to mix.
Laws have been passed REPEATEDLY, requiring 2/3rds authorization, i.e., for overturning many bad public policies. In retrospect, it's a shame we lack similar laws for tax cuts for the rich.