Most people aren't talking about how they're going to calmly consider the situation and then hit the person. They're referring to the fact that by the time they notice, said individual is going to be too close for a spider that size to get anything other than a fight or flight reaction.

Buuut yes, don't go slapping things on people or something, guys. It does tend to cause more issues. If you absolutely have to hit, do more of a swat away rather than a slap into.