Is it bad and damaging if you keep on pressing the home button of the iphone 5s? Should you always use assistive touch?

I dunno a college classmate told me that the iphone would breakdown and malfunction if its user always presses the home button

If it is bad, why is it even there?

You're doing fine and your friend is an idiot. The home button is meant to last as long as it has to.

Depending on maintenance the Home button could eventually break down. I've had 6 iPhones (5 with Home buttons) but I've never had that issue with them. I would only use Assistive Touch as a replacement should the button give out.