I think "controversy" is the wrong word. The idea is more along the thinking of "horses for courses."
When a customer first comes into a shop & says something along the lines of: "I want a mountain bike. I want a good one." But the implied mannerisms of speech & body language also suggest they really don't know a lot about mountain biking, they don't know what a mountain bike costs, or they intend to ride recreationally on the weekends, don't intend to jump, & there is a budget of some amount, then answer is obvious: A hardtail will meet all their needs. It won't blow their budget or scare them off with a wicked price tag. It will save them a bunch of weight, complexity & maintenance. It will also help them to work on their skill & they will also have a ton of fun.
If the bike bug bites & they find they want more, the customer will be back for a much more capable machine & have the skills to use it. If not, then the hard tail was the right bike for them.
The term "over biked/under biked" is over used, but the point is that falling into either camp is not as fun as having the right bike for what/where/how you ride. The right bike is a moving target.
One of my coworkers has a single speed hardtail, another has an e-mountain bike, one has a the most expensive full carbon & lightest full suspension the factory rep could provide (& then went about saving pounds further,) & I rock a late '90's hardtail. We all do ok. There is no equipment controversy among us, only who has the skill & who crashed.