Well, I'm a native speaker not a language teacher, so I'm not 100% sure, but I think part of the reason that you can't leave out the e in "es" here is that "hassen" (to hate) ends with an "e". All the examples where you can shorten "es" that I can come up with right now end with an consonant.
In any case, you can ignore the option to shorten "es" in vernacular German too. It's not as ubiquitous as the English shortenings of verbs like "is" and "are". So if you're unsure do that.