People who use artificial sweeteners in place of sugar tend to be heavier than people who use sugar, thus we can conclude that artificial sweeteners are detrimental to weight loss efforts. this is an example of:

That is an example of misuse of cause and effect  because both sugar and artificial sweeteners are detrimental to weight loss effort.
Sugar and artificial sweeteners tend to contain empty calories, that will be stored in our body without giving the sense of 'being full' like healthy carbohydrates such as wild grains.