This is where the idea of "personal responsibility" is useful for liberals. Flatly admitting that they want a desperate underclass is too mask off for them to feel like good people so they invent a way of blaming individual victims rather than the economic system.

The poor has a theoretical opportunity to pull themselves up by the bootstraps so when they don't do that it's really their own fault. Of course that theoretical opportunity doesn't translate into actual opportunity for most people but that's fine, as there's enough window dressing of meritocracy to make the opportunity look real if you are careful not to go into too much detail.

This is also the reason why liberals hate discussing real-world examples. Their logic only works in abstract thought experiments where they get to control the variables. Saying that everyone has the opportunity to succeed is a lot easier than saying that Bob, who has a set of very concrete and undeniable material conditions, has the opportunity succeed.