My brother thinks I am wasting my time by lifting weights. Do you think lifting weights is a waste of time?

My brother did bring up a good point. He said, "You're just wearing your joints down. Once you stop doing all of that heavy weight lifting, you lose your gains real fast. All of your hard work goes to crap. You have to keep lifting weights for the rest of your life to keep your gains. Do you really want to lift heavy weights for the rest of your life?" I didn't really know what to say to that. He is right. I knew some guys who were seriously into strength training and weight lifting and they lost all of their bulk and strength within a few months after quitting. And Arnold Schwarzenegger recently said he looks terrible and his body feels terrible because he is getting old. So, in a sense, I guess you could say all of his weight lifting earlier in his life didn't carry over and benefit him in his old age. So should I keep lifting weights? Will this really benefit me? Is my brother right?