If you have some vague general notion that equality is a good thing, and you believe that people ought to get an approximately the same reward for an equivalent amount of effort, then a capitalist enterprise, in which a large number of people toil for a modest reward while the owner of the enterprise collects a far bigger reward, is morally indefensible. [...] I’m not saying there is nothing more to leftist thought than that – I’m only saying that there isn’t much more.

I have to disagree with you here. I'm with wasoxygen: reward shouldn't necessarily be proportional to effort. But I'm still a socialist. I have no concern for whether people are paid "fairly" or not - quite frankly, that's their problem, and most people are capable enough to negotiate fair salaries, assuming they have a salary. My concern is rather that we ought to ensure that no person is allowed to die of poverty. In brief, I believe that one person's right to life is more valuable than another's right to total property ownership. So how do we establish this social insurance? Through a universal basic income. My leftism has very little to do with any notion of equal pay for equal effort.