If you don’t take a false idea seriously, you’re more likely to succumb to it. It’s easier to mock a false idea in the company of likeminded people than to take the time to examine the idea carefully. This is a mistake. We, as Christians, have nothing to fear. The truth is on our side.
Avoiding false ideas altogether or misrepresenting them as straw men is dangerous. The world hasn’t bought into false ideas because they were never plausible or without some foundation. False ideas tend to have an aura of truth, which is why millions of people believe them.
If you grow up thinking a false idea - like evolution or relativism - is just plain stupid, and you discount it, you won’t be prepared when you come across an otherwise intelligent person who believes and advocates for it. You’ll be caught completely off guard. In fact, you’ll find out there are real reasons people believe these ideas; and if you’ve never heard their arguments, they could sound persuasive.
Not to mention it’s disrespectful to people who hold these views. Ideas don’t exist in the abstract or float around in the air. They’re believed by people - image bearers of God. Though someone might hold a false idea, we should still treat that person with respect and dignity. Learning and understanding false ideas will allow you to intelligently converse with people who hold these ideas, but to do it in a way that shows you respect them, as well. That’s a characteristic of an effective ambassador for Christ.
I’d encourage you to read more about this principle and see an example of how I applied it in a previous post titled “Inoculate, Don’t Isolate.”