Boating is about fun. "boating is about fun and if wearing a life jacket makes boating more fun for me, i expect you to respect that." that's enough but if someone still asks why, tell him or her that if you fall overboard and get knocked out in the process, you often die. A life jacket gives you a chance to be saved. Whenever i sail on a large lake or sea or alone, i wear a life jacket and I have been sailing 40 yrs.
Protect yourself! Just because one is wearing a life preserver on a water vessel doesn't make them any less of "cool" than the next person. In fact, in my book, it makes one far smarter. The intent of a life preserver is to protect one's life in the event of an unexpected boating incident especially one in which the victim is knocked unconscious and can not swim. This can happen to even the best swimmers.