“Allowing zoom” and “being responsive” are not two states at odds with one another.

Preventing zooming is a serious accessibility issue and it makes the content worse for every user.

If you’re properly setting responsive widths, a large enough base font size, large enough input text size, and using border-box for box-sizing, things should just work except for cases where you’re absolutely positioning things or telling them not to word wrap and they are wider than the viewport.