First of all, is it worth mentioning that את is a preposition used to introduce a semantically definite direct object, not necessarily a grammatically/formally definite direct object.
In this sentence you have כולם (kulám), which is considered semantically definite (if you think of it as a contracted personal-pronoun-including form meaning "all of them" you will see why). Hence the את.
In your example you have כלום (klúm), which is obviously semantically indefinite, so you don't need the את. As for הכל, as far as I know, while it is semantically definite (and also grammatically definite due to the ה־), the use of את before it is optional.
(I'm also a learner, that's what I know so far.)
It seems that hate is very important for Hebrews, but not for western people. When there are problems we ask for TOLERANCE. Hate is a feeling of the past, if we live in the present we don't feel hate. There are too many sentences with hate, more than necessary. In any way many people in this course love each other, including you.
That's because we know, like, ten verbs at this point! Bloody bears are learning bloody Hebrew, mate! Does that mean that caniforms learning Semitic languages play a major role in the culture of the "Hebrews"? Or just that the authors of the course had to adjust the sentences to our level and could only express so much? Ironic really, that you express such anti-Semitic sentiments whilst simultaneously boasting about the tolerance Westerners allegedly espouse.
It could include "them all", as in all of the things. For example: "Do you like apples, oranges or grapes?" "I hate them all/all of them" "האם אתה אוהב תפוחים, תפוזים או ענבים?" "אני שונא את כולם" "Everything" is הכל. "What do you hate about it?" "I hate everything" "מה אתה שונא בו?" "אני שונא הכל"