Before I even created my channel anyone I talked to about creating a youtube channel told me the same thing: "Why? It's just a waste of time, you use that time doing something more productive. You'll never be popular, you'll never make it a living." I've been doubted by my family and friends on a lot of things I've attempted during my lifetime. There will always be people who will try to bring you down for whatever reasons they have, you have to remember that it's what YOU want to do. If you enjoy creating videos then keep creating videos! I will never let people with their negativity defer me from doing what makes me happy. It's pretty messed up for your brother to say that but it's your channel, not his and at the end of the day you have the final say on what you want to do. Don't let anyone tell you that you can't do something, the worst thing you can do is give up without trying.