bs. It tastes sweet so it must have the same effect as sugar? Ok... Lots of things we eat aren't recognised by our bodies as food. That's why we poop. Also, all artificial sweeteners are not the same, it's impossible to believe they would all have identical effects on the gut bacteria. Finally, you cannot get obese without an excess of incoming calories, period full stop. The gut bacteria can only function properly, they can't make calories out of nothing. If the gut bacteria isn't right digestion will suffer, not get turbo charged.
Edit: that said, artificial sweetener use is really a side effect of our widespread sugar abuse. People want to get off the sugar so they go for the artificial stuff. Which is ok, it's certainly better than consuming 25% of your calories from sugar, but really it should only be a temporary measure.