The reasoning behind having diesels on the line can be summed up in one word: Money.
Diesel's don't cost a half million dollars to overhaul, and they don't require the constant attention that steamers require.
There is an appeal in stating that a rail line is completely steam, such as the D&SNG claims. I can understand that line of thinking, but C&TS does not have the resources in manpower nor money that D&SNG has.
One can say that historically, diesels never operated over the C&TS, but that would not be totally correct. D&RGW experimented with several diesels as you are all aware, I'm sure.
Jay, consider it this way: If the diesel can save some money, that money can be put toward restoration of steamers.
Jim Burrill