Not utilizing a technique isn't promoting bad technique...if we were to say, "dont practice and use it in a tournament" then it would be another issue. In general I have been taught to not try thrusting...especially not when on your knees and eventually you are going to hit someone in the crotch.
That's part of why I think the SCA combat system is so far off from the historical sources. Thrusting is a MAJOR part of proper WMA/HEMA combat. You remove grappling, you remove striking at or below the knee ... and if you remove thrusting too? You're left with such a subset of valid techniques you can actually use that it resorts to creating modern techniques to take best advantage of the rule set of the game (like getting in close and wrap-shotting somebody's butt).
And that's totally fine if it's what you want to do. People in karate tournaments don't actively try to break each other's necks because it was historical. It's a modernization. I didn't feel like I was participating in historically based combat when I did SCA heavy. I also didn't feel like a samurai warrior when I took karate. Both were actually pretty fun, even though I didn't excel at either one.
Not utilizing a valid technique in a situation in which that valid technique SHOULD be used is, in my mind, promoting bad technique. I'm still completely blank on why not to thrust. Thrusting tips are on the weapons for a reason, right? Are you sure it wasn't "don't thrust at areas of inheritance" and not just a blanket "don't thrust at all"?