Well in the case of Billy Turner, he has tremendous talent and the Broncos' OL is godawful, so they are hoping the light will come on for him. That is not the worst move by them.
Jamil Douglas is by all accounts a pretty solid guy, he just wasn't performing well. In his case, I do believe that we handled his position poorly. He was a college left tackle who was projected to be a left guard in the pros, and we started him out at RG and then moved him to center, where he had never played in his life. He's a player that I think can definitely improve with time and be a solid lineman for someone in the future.
Dallas Thomas sucks and the Eagles are stupid.
In the case of Turner and Douglas, we may feel like those are potential solid NFL players, but the fact is that they were horrible when we cut them, and at that time we needed players who weren't horrible.