I think the security point is better because

1) there are less of them usually then there are boarding gates, considerably less of them, so that means less people to do the checking.

2) You have the people there that have to check boarding passes and ID's anyways to see if you are allowed past that point

3) It's the security people, not the airline people that are doing it there

4) This way nobody who doesn't have an ID and a boarding pass (how hard was it for any of us to make a fake receipt if we needed one) can get past

5) I can put my ID away and leave it away until I get to the rental car counter no matter how many connections I have.