If people hated slavery why would they go against Abraham Lincoln?

Opinions about slavery vary from person to person, culture to culture, and time to time. They are not always logical, and they don't always agree with actions. Besides that, it is a mistake to read your own morality into other people, cultures, and times.

As for Abe Lincoln, well, a lot of books have been written and the history doesn't always make sense. All you can do is study what you find and see what conclusions you are able to form.