I used to bleach my hair all the time and when it says that you aren't supposed to apply directly into your scalp, it's only warning you to not work it into your head like you with when you're using shampoo or something. When you get your hair bleached at a salon, they'll generally "paint" it onto your hair with a brush. But yeah, just dumping it on your head isn't too awful.
As for the bleach itself, since it actually kills your hair, yeah, it totally unhealthy for the general well being of your hair but if used sparingly it isn't too awful, like having a cigarette every now and again vs having a cigarette every day. One will cause some serious issues long term where as the other just kind of isn't the best thing to do to your body. I'd have to actually have a box of bleach in front of me to give you a straight answer of what's in bleach but I think a major component is Hydrogen Peroxide??? This is just off the top of my head though.
If your worried about your hair at all, I would just suggest laying off the bleach for a few months (maybe a year if you use very frequently because you've got to let your hair recover and regrow some), dying however doesn't have the same corrosive effect on hair as the bleach does so you can probably still get away with that.