Oh I fully agree. They are a patchwork of different value systems that feel (and indeed are) crushed under the weight of general movements of society.

But don't underestimate on how much they could actually cooperate on when it came to actual policies. The left as fragmented and sectarian as it was and still is in some parts of Europe, has been very successful in influencing the intellectual and social norms not only laws in directions that when looking at history seems favourable to most involved in the wider political groups.

The actual result of economic inequality may seem as worse in the past by many, but had they not been active it would probably be much worse (as judged by their value systems).

Or look at the mainstream right. Christian fundamentalists, token libertarians and hawkish Neoconservatives... would any of these had it in itself given lots of power create a society compatible with any built by the other ones?