>when your thread character limit is bigger than your daily active userbase
Slide threads are useless when you can have threads on the most active board stay on page 1 for 24-36 hours with no bumps. The more restrictive you make things, especially unnecessarily, the more you're discouraging newfags. Just my opinion.
We would discourage newfags that make garbage threads. That's a good thing.
Personally, I think the reaction to garbage threads is enough discouragement to keep them from making more than one. I consider thread quality to be more in the activity it stirs up among other users than a specific amount of content in the OP.
It's not like total garbage threads aren't purgeable.