At least I come to this question quite a lot.
While quality is better than quantity, it's sometimes hard for people new to digital marketing to understand.
I first state that sending to EVERYONE can lead to bad practice (hard bounces, soft bounces, unsubscribes, and worse marked as spam) AKA ending up in a spam folder or getting downgraded on your digital reputation AKA getting more limitations.
I also add that it's not like traditional media where you could pay for a space (commercial on a soap opera) and people have to see it. With digital platforms, the equation of what you paying to show your message includes people's reactions and that is where operating in negative can occur. From there I give an example I'm pretty sure they have lived with a YouTube ad that the only thing you think of is when you can skip and end up hating the brand (not buying it on purpose).
Would love to hear what you answer to this question that keeps popping up. (and forced to action in some cases)