People about Cosplay...
First of all, cosplay isn’t just about playing dress-up. Cosplay is a whole lot more than that. Good cosplayers will act like the character while in costume or move like the character. Serious cosplayers won’t break character when they’re in costume. It’s a little bit of acting too. But it’s a culture that’s meant to be fun.
You see, cosplay is a couple things. First, it’s a service to the fandom because other people get to essentially see their favorite characters in the flesh for a couple hours. And this is especially true if you really fit the character. But it’s a lot more than that. It’s a chance to be someone else for a little while. When you put on cosplay, you get to leave your life behind for a little while. And for the people who make their own costumes, it’s a chance to not only show off their knowledge of the character, but it allows them to show off their costume skills and say “I made that.”
So, there are a lot of different appeals to doing cosplay. Besides, with all the photos that people take of you in a day, it kind of makes you feel like a celebrity. :)
The only place it should really matter is in competition. Don’t enter a workmanship based contest with something that you bought or commissioned, and don’t take credit for the work of others.
That said, some contests have a category for commissioned or purchased costumes, you would be fine if you entered there.
No, it is perfectly normal to buy a cosplay costume. Even professional cosplayers buy or get the costume made from someone else. However, making your own costume has a different thrill to it.
What is important though, is how you carry the costume and how much fun you’re having while cosplaying.
As for “devaluing someone’s participation” goes, some may feel that your cosplay is superior to them, when they took more efforts. However, it is not supposed to be that way as these things are done for fun.