I understand that, but you really need to have the real world experience, or at least a bit more than you have now which is near to zero, before you can feel the context of this. As with so many other things it is not black and white and there is not one right answer. The answer, as usual is, it depends. You cannot feel this without any real world knowledge. I would not tell a general contractor with 10 years of building contracts under his belt that his way of setting rebar into concrete is wrong if I've never done it, regardless of any books I had read on construction science. Likely HE knows the context of his work better than I do.
Using a belt is a skill. If you don't practice the skill you don't get good at it. So, from that standpoint, if you compete with a belt you need to practice with it to get the most out of it--this is most applicable to powerlifting instead of olympic weightlifting. However, there are other valid reasons for wearing a belt below your 1 rep competition max EVEN if you do not have any orthopedic problems.
My brother squats 5 days a week. This week he squatted 6 days a week. It went like this:
Monday 5x5 back squat.
Tuesday 5x5 front squat.
Wednes 3x5 bad squat.
Thursday 3x3 front squat.
Friday 3x10 back squat
Saturday Overhead squat 1 rep max
Oh wait--this was in addition to training the olympic lifts 5 days a week. He doesn't have any orthopedic problems with his back though. Are you telling me he shouldn't wear a belt? You do not have ANY conception about the type of effort this takes because you have not put any serious effort into real weight training.
The majority of olympic lifters do things similar to this, if less volume and slightly lower frequency in squatting. There is no reason to make the comment you did. I realize it was done with good intentions, but quite frankly there is no way to blanket statement a piece of advice like "don't wear a belt unless it's a competition max".
This is completely different from a weekend warrior whose core is made of jello and who does not serious pulling volume, who needs the core strength. Or a bodybuilder looking to rep out a set. Or a crossfitter doing 70 lb kettlebell squats for time. With all respect, the fact that you do not understand this is proof that you need to spend more time in the gym and less time reading, and less time giving any advice.
The next time you are in the gym, try putting 400 or 500 pounds on the squat bar and just unracking it and holding it. Don't try to squat it because you will die. Please hold it for 20 seconds, and then try to understand why people who squat that much weight want a belt, even if it is "only" their 2 rep max. I'm not trying to crush you but you HAVE to understand these things and that shit only happens by really going after the lifting instead of reading. I understand you are trying to help, and that is laudable. But you do not have the tools to help people, and this isn't a criticism, it's just fact based on your history. If I want to bench 500 lbs, I am not going to listen to the guy who can't bench 200 lbs. I am going to listen to the people who are a bit stronger than me, or at least at my level for what is helping them. You have to get genuinely experienced before you can start to help, as much as you want to help.