I think popups on page load are more of a symptom of short-term, myopic thinking than anything else. This type of thinking is strongly encouraged by always trying to live up to quarterly projections - "Did Sales meet their targets?"

Popups exchange long-term trust in your brand for short-term profits. Of course it's the case that if you pop a modal in front of everyone, your conversion stats will go up. But potential life-time customers who have faith in your brand and believe in your mission will lose trust in you quickly and probably never sign up in the first place.

For me, it always comes down to the primary rule of UX: if you wouldn't do it IRL, don't do it online.

You can ask for someone's email if they look like they're interested in something you're selling, but don't ask for it the moment they enter your store!