The sweeteners affect some people (me for one), and the sweet flavour affects the body's insulin production, appetite and sweet tooth. Haven't come across the fatty liver thing. Will look it up.
There is some evidence that drinking artificial sweetener laced drinks leads to less weight loss and/or more weight gain than not drinking them. Sorry I don't have the articles to hand - this evidence has been around for years.
Personally, I avoid all artificial sweeteners like the plague. I use erythritol, as little as possible.