They started as a just people with similar ideals. They didn't label themselves Goths. Other people did.
And if you choose to dress the same you can. The point is that people should be allowed to dress however they want. If you want to all dress the same, that's fine. People shouldn't feel obligated by society to be the same. That's all.
And the point was you're treating two completely different groups of people the same, and being really condescending by acting as if they are a bunch of whiny kids and that you know better.
You're making statements based on stereotypes and archetypes that aren't true. Emo is a style of music. Goth is a style of dress, and a ideology. Neither has anything to do with the personalities of the people involved. It's a stereotype that "emos" piss and moan about things. It's a stereotype that goths are all depressed. Both were made based on a few people, and made by people who didn't know what they were talking about.