Having worked with metal, I am well aware of how soft steel really is. When Ruger incorporated the plunger tube with the frame, they eliminated one of the weak points of the 1911 design. I hated that non-traditional feature at first, until I gave it more thought. One less thing that can go wrong as per Murphy's law.
Whatever you need to be "right."
I've talked with a number of custom pistol smiths about this issue. Their opinion has been that if the plunger tube is installed correctly - it will not come loose, and one of them has a 1911 with 100,000 rounds through it with the original plunger tube. Could be luck, could be his opinion on plunger tubes is correct - your choice.
However, I do agree that the integral plunger tube as part of the frame is an evolution of the design that makes a lot of sense and can eliminate a potential failure point completely.