One experiement nutritionalists/scientists love to do is take people and have each group only use sugar/splenda/whatever. And then they have results at the end of some period with sugar being the "better" chemical.
However there is never control on what they eat.
Someone drinking koolaid with sugar, but eating grilled chicken, broccoli, carrots and potatoes vs someone drinking a sweetner with mcdonalds Big macs, 2 large fries and a small sundae.
Guess which diet is healthier? The sugar one. However if you equalize the meals. And equalize how much of Splenda vs sugar is eaten/drank. I bet over all health effects will slightly lean in favor of splenda. However I agree the taste of it sucks in comparison.
the true issue with sweetners is? It psycologically tricks people into thinking they can eat more because of drinking less sugar.
Not to mention, without significant control of oneself, it still causes a rise and fall in actual blood sugar, which typically results in feeling hungry again sooner than one would normally. If one listens to the first gut signals, you would eat more. If one waits a fair bit of time after first getting those gut signals, the body will typically generate new signals that signifies satiation.
It takes a fair bit of mental mind games in terms of eating in general, and playing the sugar/sweetener rise/fall game. Our body is keyed to not give two shits about what we think mentally, but rather works on up to the second information gleamed from chemical reactions produced on the gut, which is typically a react first, figure out later sort of thing. All that is because it doesn't care about our figure or what we do or don't have right in front of our eyes, it just wants to ensure it has enough food to survive. And typically, it's a glutton-sort of process, because "it" does not initially value anything regarding the external situation and what the brain ultimately understands, rather... it only knows right now, right this second, and doesn't understand time, especially in regards to long-term planning.
The gut simply wants to ensure we can survive. It also has no concept of false sugars. Most of them, save for sugar alcohols (I think) and stevia, tend to trick the body into actually thinking real sugar is present. Which one may think is good, until you realize that means the body begins shuttling sugar about because now it thinks it has sugar "on-deck" so it can put reserved sugar "at the plate" instead of calling in the pinch hitter to stave off any unnecessary burning of reserved energy.
So after a heavy dose of a sugar substitute like sucrolose, blood sugar and insulin activity tend to increase (I may have butchered that part...), which means it will drop later, which causes either (or both) hunger and fatigue. Which, the natural reaction for our body tends to be "okay, we need more energy. FEED ME!"
Which, for anyone who has thus far failed to manage a healthy dietary intake, and is resorting to diets (or, for those who must carefully monitor blood sugar levels), this can be a very bad thing. For the former, it means they'll eat more unless they voluntarily suppress their desires (and ignoring the initial instinct); for the latter, it can be hazardous.
Looking back, I probably have a lot of that wrong at the specific level, as I was trying to spell out a generalized picture (possibly without success on that front either).