Maybe the levels of hate that liberals have for conservatives and conservatives have for liberals is the same. However, conservatives also had and have hate directed at other groups of people, like minorities (e.g., slavery, minorities getting the right to vote, minorities gaining citizenship, etc.), women (e.g., women's right to vote), homosexuals, etc.
Now I think that liberals probably have a hatred of groups like racists and so forth, but I think that most people would say that hatred of racists is acceptable, but hatred of groups historically opposed and/or hated by conservatives isn't acceptable.
Thus, the math comes out to conservatives being more hateful than liberals.