I've heard all season that we have so many new players it will take time to gel. That we're low on confidence. Lets assume those are true for a second. Then surely thrashing Fulham at home, playing your best players together would help both issues. And playing a weak team that loses is going to hurt both of those issues.
You can't always be so worried about injuries. Gerrard and Suarez could both go up for a header in the first minute, clash heads with eachother and be stretchered off. I hope nothing like that happens but you can never predict these things. I don't see much point in resting all these players.
They didn't need to get injured. Why do you think Reina didn't play? Perhaps his red card prior to the last cup game opened Kenny's eyes to the problems with depth in the squad so he wrapped everyone up in cotton wool. The expendables played. He could probably have started Sterling, but I think Kenny wanted to see if Maxi had anything to offer. When Maxi showed he had nothing, Kenny pulled Kuyt (probably for the bench/extra time/penalties on the weekend). The Enrique change was puzzling, but perhaps that too was a test or an experiment.
Make no mistake - this was a nothing game in Kenny's eyes, one he felt he could afford to sacrifice. But I think he was annoyed that the players had no heart for the game - that 11 should still have had enough to see off Fulham (who are atrocious away from home season on season) given how many games they have all played this season (except for Aurelio and Doni).