Trench Footing with Perimeter Drain

Hi guys, I'm a general contractor and I could use some help with a detail involving a trench footing with a perimeter drain on a project I'm working on currently. Admittedly, I have not built many structures on a crawlspace, however, when pouring trench footings in the past, I've been told that it is never a good idea to excavate the virgin/compacted soils on the sides of the trench footing as it could sacrifice the structural integrity of the footing. Essentially, the virgin/compacted soils on each side of the trench is what helps to stabilize the footing, thus excavating the soils to install the perimeter drain and gravel is never a good idea. I would love to hear the group's thoughts on this. Subject detail is attached for reference.