Telling someone with a learning disability to 'study harder' is like telling someone trying to find their way in a dark room to just 'look harder.' What they need is a light, not more effort in the wrong direction.
Not every hardship is a result of a personal moral failing. In fact, MOST aren’t. Life is hard.
Calling someone an idiot or claiming there is a widespread learning disability that makes most people idiots is pretty ableist. If they're wrong, or they're jerks, that's probably the thing you should focus your commentary on.
Idiot is a slur that implies some degree of learning, intellectual, or developmental disability, and is often used to other non-disabled people by painting them as having such a disability. This cements the mental habit of treating such a disability as a form of inferiority, and of dismissing the views of those who are perceived as having such a disability. You are tearing down a whole group of marginalized people who are innocent bystanders when you use a word for them as an insult for others.
It's the slightly less offensive sibling of the r word. Please don't use it. Focus on behaviors, not abilities.