Again, just because it's not pro-Trump doesn't mean it's automatically alt-left, or liberal, or Antifa. These words all mean things and generalizations don't really benefit anybody. How about if I say what about all those cops killing blacks, or what about all those white people being racist? The "alt-left" has it's fair share of ****heads, although I don't know of anybody that actually calls themselves alt-left as it began as a way to deflect attention from the alt-right. I would urge you to look more into exactly what the alt-right stands for before brushing them off. Start with Richard Spencer since that it typically where the modern alt-right begins.
As far as protests and marches go--regardless of message or side--I'm always in support of people practicing their constitutional rights.