Hey Justin,
I'm sorry the way your tattoo artist reacted to your wanting black work done made you feel so bad. When someone tells you something you're into is stupid it hurts so much. I'm seriously considering getting a tattoo when I'm 18, but whenever I try to talk about it with my family (since my cousins are my best friends) they shoot it down and try endlessly to talk me out of it. It hurts when they tell me I'd be ruining my life and my body, and that it's a stupid idea so I totally get why it bothers you. Especially when it's their opinion they're using in the argument. As you said before the tattoo artist told you it was stupid and they personally hated it, but that's just their opinion and it doesn't make yours wrong.
However while it's important to do what's going to make you happy, you should also take the time to consider others opinions because they see things we don't. Especially with something so permanent, it's always good to get some different perspectives on things and really consider them. That's why I really think you should consider the blacking your arm out with a sharpie that Essa suggested. You may be completely right that you love the idea and will love it, and if so why not just try it for a few days without it being permanent? What's the worst that could happen in trying it? Either you realize you really don't like it that much after all, or you absolutely love it and are completely committed to it.
In the end though it needs to be your choice, and not because of what other people want. You need to live life for you and you alone. If you're not happy with something don't just go with it because everyone else likes it. That will make you miserable in life, and that is the worst way to live trust me.
I hope you figure everything out, and would love to hear what you decide!
Hope this helped,
Kay