I assume you want to draw freehand with the Brush, but want a "basic" setting. This is not possible, because that "basic" setting doesn't work with the Brush tool.
Use the Pencil tool instead if you want to draw freehand, with a "basic" stroke.
The interface is a bit confusing in regards to this, and Adobe probably needs to do some work to address the problem of "basic" still being a selectable option when using the Brush, despite the fact it won't work with the Brush tool. Of course, Illustrator is not user friendly (never has been in fact), but I suppose that's the cross we have to bear until Adobe improves it.