Grease is great is theory. In reality, guns get dirty when shot. Has anyone noticed what happens to grease around dirt? It grabs it like a magnet. So what happens when you mix dirt and grease? It becomes a gritty paste, which is just like lapping compound. Would you lubricate with lapping compound?
Oil will also attract dirt but the dirt still has the ability to move around, rather than to be trapped.
Grease isn't bad. I have some looser autos that I have used it for. This gives the dirt more room to move and makes the slide feel tighter. However, for a tight 1911 I only recommend DW rail lube, FP-10 or Militec 1. There may be other good choices out there but these have been proven here.
Oils such as Rem oil, Hoppe's and the like, I only recommend for the surface and small moving parts.
Also, Beware of gun cleaners such as CLP that is not polymer safe. Though our Duty finish is not Polymer these "gun scrubbers" will damage the look of our Duty finish. Using oil as a cleaner is all you need. A little oil, nylon brush and elbow grease does wonders. Kroil, btw, is a great oil cleaner. It will even remove copper fouling from your barrel. Bench rest shooters have been using it for years.