Academic work / study in K-12 should be difficult enough to stretch and at times struggle without causing unhealthy stress. That doesn't mean one can't get straight As but one should have to stretch to do so.
The danger in not having stretch and at times struggle in K-12 education of course is that highly likely they will in college / university and a Freshman year when they're not among a lot of friends, family, etc. in a different environment than they're used to is not when you want them to get their first dose of academic struggle and figure out how to deal with it, that's when you want them thinking to themselves, "Okay, I've been though this before, I know how to deal with this, I can do this."
