You don't have to answer the second line, really you don't. I have it and I love it. I recall while growing up that I needed to get in touch with my mom to let her know something, she was always on the phone, it never failed.
With three kids I insist o having it. I would hate to be on the phone having a long conversation about something and them need to get in touch wit me and couldn't. Also if I need to get a hold of them while I am out, and they are on the phone, they can tell their friend to hold on. Sometimes it is an emergency. One time DFIL had a stroke, I was on the phone with a friend hadn't spoken with in years, if I didn't have call waiting it probably would have been a couple of hours before we found out.
I do think it is rude to switch over to another call unless it is an emergency. Both hubby and kids know that if it is an emergency and I don't switch over to them, they just call right back and I know to answer the 2nd line. I would gladly give up some other form of technology before I gave up this one.
I don't understand why the attitude about call waiting. Sometimes needing to get through to someone is an extreme emergency.