Those people are clearly not there to support you and they are probably people with bad intentions. Also, remember that some people think they can put any cruel/senseless thing on Youtube because, "It's the internet," and they don't understand that there are real people with real feelings on the receiving end.
Don't let anyone feel like you are forced to do something. Your channel is there for you and you are in control of what kind of videos you put out. Don't give up Youtube. One day, you might look back and regret quitting something that was so special to yo; and that is what Youtube should be about--something special to
you.
Since you have comments only upon approval, it can be hard to control what kind of things you see and don't see, but unfortunately unless you turn off comment all together you might have to deal with reading the occasional sadistic comments that you get sometimes.
Chloe, you might want to consider only looking through the comments to approve them when you are in a good and strong emotional state. That way, if you encounter a foul comment, you won't be drained as much as you would when you are in a not-so-good state. Even I choose not to reply or read comments sometimes when I am in a negative mood.
EDIT: One other thing you might want to do is if you see any comments that make you feel uncomfortable, don't bother replying to them; just block them...