Katydids will eat pretty much the same things as Grasshoppers. I too for the most part ascribe to chain of life ** and let be most of the time. Not all. This summer grasshoppers have been horrible - most I have seen in decades. They decimated scores of young seedlings - clear cutting many. So I eliminated a bunch over a couple of week period when ever/where ever I saw them. But I usually just leave them be.
** I even like hummingbird moths more than the excess of tomatoes that I can not keep up with in giving away. So when I find a tomato or tobacco hornworm - they stay and I donate the plant to them for awhile. Must admit it was hard watching one absolutely devastate a Contorted filbert (Harry Lauder walking stick). Guess what - it is releafing out and the hornworm is long gone.