That's true. Peroxide can kill you if taken internally. Besides the fact that it can damage your tissues, there's some concern about bubbles of gas that can do some kind of damage to you, perhaps even kill you. It's been a while since I've read about this. I looked it up when I was considering using it as part of the candida treatment.
But peroxide has been a life saver for me as far as my tonsils and throat go, because I've used it to clean the crypts in my tonsils (before I finally convinced the doctor they needed to be removed) and now use it to clean the back of my throat to clear it of post nasal drip.
Before I started doing that, I had an infection of my tonsils or throat every month. Finally, I began dipping q-tips in peroxide and cleaning the tonsils two or three times a day. Poof. No more acute flare ups, but I still had a low level infection with a chronic low grade fever and a feeling that the tonsils were slightly swollen (I could feel them, in other words).
The lab tests on them after they were removed showed evidence of long term infection. As the doctor so eloquently put it, they were nasty.
Just my opinion, peroxide is very useful, but should be used carefully.