It's more like calling someone a whore versus calling them a prostitute. It's not less black, it's less specific.

"Fraud" is a specific legal conclusion that requires a certain state of mind. Someone just reviewing a paper isn't in a a place to level the highly specific term "fraud" versus the more general term "error" because he doesn't have any evidence about the author's state of mind.

I do believe that the usage of certain type of language depends from the place and the time. So from my point of view, it's one thing using "fraud" in scientific paper and completely different story using in a community platform. Should I write on my web site, just like I would talk in the court?

Its the not because its a legal term, its because its a highly specific term. You can freely call someone a whore. If you call them a prostitute, you had better have some evidence that they actually trade sex for money.