There is a significant view on the left (at least on Twitter) that liberals are evil. I don't think there is an equivalent view of leftists by liberals. Broadly speaking my critique of the left is that they are non-rigorous...both their politics and policies are largely conjecture with no real support (often ignoring real life evidence that their policies, like rent control, don't work). End of the day, a lot of it comes down to mistake theory vs. conflict theory.
As to your examples...the Dems didn't have 50 votes for a $15 minimum wage, so Kamala Harris is irrelevant. Manchin won't support a $15 MW because a $15 MW is bad policy for West Virginia (and a lot of the country tbh). And the Dems have no control over Manchin, no leverage. And you can't really motivate him with threat of a primary. As far as I can tell the left picked $15 minimum wage for purely marketing reasons, I've yet to see anything that shows why $15 is THE economically preferable national rate...that it maximizes good things or minimizes bad things. The CBO suggests that it will on net lift hundreds of thousands out of poverty...but it will consign more than a million to unemployment and even deeper poverty. Using the minimum wage as the main tool to improve standard of living is just really bad economics. Better a lower federal national wage ($10-12) with higher state/city MWs where median wages are higher, and then use other policies like EITC or Child Tax Credit to raise the living standard of people at the bottom. A $12 national minimum wage would get it to the historic high point controlling for inflation. When taking into account all the state and local increase that have been passed, the national average minimum wage is already at the highest it has been.
And even though Biden isn't using executive orders to wipe out all student loan debt (which would be bad policy), he has already used it to target student loan debt of people who attended scam for-profit colleges and for those with disabilities that have put them in default.
As to "kids in cages," you can't just open the doors and let the children wander the world. Biden is putting a lot of energy into building up the capacity for more humane housing conditions and capacity for placing the kids with family to facilitate the process, but those things don't get put in place overnight. The government is like a shipping barge, you can't turn it around on a dime, and sometimes it gets stuck in a bank and screws up international trade for a couple weeks.