Personally, if i saw groups supporting Bernie Samders, antifa, BLM and others, peacefully coming together under the banner of 'Alt-left' i doubt this would he a bad thing.
Standing for an end to racism (BLM), improved access to healthcare (single payer system in the US, which i'm sure Sanders supporters would love), and a (peaceful) solution to Trump's fascistic government (antifa?).
What are the things Liberals hate the most? Progressive democratic socialists, like Bernie? Fair access to healthcare? Redistribution of wealth to pay for preemptive trestments (which reduce overall cost of healthcare). A massive reform of the criminal justice system? Read about prison abolition, about restorative justice, about the size of the prison population in the US (compared with other developed countries). Read about the prison-industrial complex, ie privatised prisons.
Training to reduce police brutality and racism? Investment in education?
Protecting the environment, and action against climate change? (Or is the a liberal policy??) an end to austerity policies and bank bailouts, which have hurt working class people across the 'developed' world.
What am i missing?