Here's why. My sister and her family were unbelievably "toxic." Yet year after year after year after year I stuck with them. I loved my nephews, one in particular. After our mother died, and during my first "battle" with cancer they dumped me. I guess (because I'll never know) it was because I was so toxic. There had to be a better way. I am brokenhearted over this and it will never be healed. So, who's the toxic one? Everybody, I guess, depending on who you ask.
Yes, there are clear cut cases. Then again, not always. It's an easy claim to make and it makes a lot of folks feel better when they unceremoniously get rid of someone who may need them.