There is an entire category of foods meant to be eaten as 'meal replacements', sold in grocery stores etc. Google it. Soylent is perhaps the best of the lot; its tailorable to your activity level etc. And yes you can eat Soylent for an extended time and feel better than if you ate McD's all the time, which millions of people do and yes, they live to tell about it.

The criticism is overheated and silly. Eat what you like, everybody else does. Lets cut out the unsolicited advice and scare tactics, it sounds silly and timid.