This is something I've put a lot of thought into the past couple of years, and a few little soundbites I've come up with during my imaginary shower interviews are:

1. If you don't have Quality Assurance, then you have Quality Uncertainty.

2. QA is a full time job. If you offload the responsibility of QA to the engineers, then you're giving them 2 full time jobs. So unless they're working 16 hours days (even if they are tbh), you aren't assuring quality, you're compromising it.