Vaccines do provide immunity, there is a wealth of information and studies to prove this. Are they 100% effective all the time, no.
Vaccines do not tear down the immune system.
I'm very glad your friends children survived whooping cough, but that in no way negates the death of children who continue to die of this horrible, and preventable disease.
Personally, I would not want my child to suffer through diseases, that could have very damaging effects, if they didn't have to. My own daughter had a very severe case of chicken pox, (before there was a vaccine available), she has had very bad scarring, and has suffered lung damage because of this disease. My friend's son came very close to being blinded by this same disease. Thankfully my grandchildren will not have to suffer through this disease.
As I've said before, it is up to individuals to decide whether they vaccinate or not. People need to decide whether they want to take the risk of their children, or themselves, contracting these diseases, with the possibility of adverse outcomes, and whether that risk is greater then the risk of an adverse outcome from a vaccine.