It works the other way around, you need to prove that gravity doesn't exist. We operate under the assumption that it exists until otherwise proven, not the other way around. If we assume that gravity doesn't exist and there is no other theory to fill its place in the meantime, the most basic of things on earth stop working. Without gravity, there is no friction, how electricity works changes, the concepts of energy change, as well as a billion other factors that you can imagine for yourself.

Not everything has a practical demonstration. Some things are limited by your knowledge, some by funds, others by time. I don't refuse to believe that airplanes fly because I can't fly my own airplane to see how it responds. I can observe airplanes flying, and listen to someone explain why it is. A child can understand that a plane flies, even if they haven't had vector calculus to understand why that is. If their explanation makes sense, I believe it. If there are any cases where what they said isn't true, then I don't believe it, unless there is a good reason for that. Without what other men tell us, we wouldn't know how to do basic math, how to dress ourselves, or start a fire. There isn't something inherently bad about listening to others. "History" is how humanity evolves. We wouldn't get very far if no one thought to tell others how to make a fire, and we had to wait for someone to figure it out in every generation.

You need to come up with a unified theory of how everything else continues working using your theory that gravity doesn't exist, and that density is what matters if you want to make your case. Keep in mind that you can't use evidence to support your case, if your theory throws out the basis for that evidence.