There are too many awful parents out there for me to believe having kids makes one uniquely qualified to make suggestions. Dismissing ideas with a variation on "you must not have kids" is a huge red flag. It's usually done by people who see kids as things to be controlled and made subservient instead of as adults in progress.
We were all kids once. We all had friends whose parents had different styles, and often we got to see how that turned out. We all have a set of relevant experiences to pull from on the subject. Maybe it won't work for you. That's fine, but maybe you could actually say something about what's wrong with the suggestion instead of issuing a blanket dismissal. Or do the polite thing and ignore it.
You can spare me the condescending "so you don't have kids" that always follows this and just move on if you have nothing better to say.