Tough to say. With United the hate comes from jealousy and preferential treatment (for their team, manager), plus the insane amount of bandwagoners, but it is offset by an underlying respect for the dynasty they created. They are ridiculed for having fans from everywhere except Manchester, more of a brand than a club these days, but not really in the same way that we are a team for Italy. When you target United you aren't targeting a city or a people, it is just a football club.
With Liverpool their dynasty was 30 years ago now, so they have a lot of fans who support the team through their parents who remember the good old days when Liverpool swept all aside at home and abroad. For me they are amongst the most delusional because for a long time they have still believed they are this big power just waiting for a break. As a club they have their heart on their sleeve, but no brains behind it.
I would separate scouse Liverpool fans with Liverpool fans in general. There are politics involved that include and go beyond football, the whole north/south divide, working class, mining strikes backdrop, and the consequences of Heysel (one thing older fans of other teams don't like them for) and Hillsborough. There has always been a sense of oppression and victimisation coming from Liverpool, so they are very insular and staunchly biased. This spills over to the wider Liverpool fan base. You see something similar with Newcastle fans, similar backdrop; extremely loyal and local proud but unbelievably biased. With them, however, they can only go so far, because they don't have the grand history to back up their pride.
Just my take on it.