whilst I don't think it compromises safety, it compromises service & the well-being of your workforce.
20-minute turnarounds are achievable if you're well trained, even if there's only one person on the gate, I've done this for both 156-seat easyJet A319s & 189-seat Ryanair 738s. The issue though, is that whilst you are efficient, you don't have time to be friendly, and sometimes you are unable to ensure that the boarding procedures such as priority boarding groups can be offered
I'm sorry but I totally disagree. You may think that pulling cards as fast as you can means being "well trained" but I do not. I do not believe that you can achieve a 20min turn-around single handedly, and only sacrafice boarding groups and a friendly service. If you have not cross-checked names on boarding cards with those in the passport, and checked the photo, then you have not done your job properly!! I really don't know how PSA's can relax, knowing that they have allowed an aircraft to depart without being 100% certain that every single piece of baggage on board, is accompanied by the same person that introduced the bag into the system at check-in!