If you have data you don't want the user to mess with, it has no business being in a config file.
So you'd rather have an in-game element like "amount of lives" or other console-like settings exposed so the user can put whatever value he wants?
Regarding things like resolution, graphic features and gameplay elements you could have a modifiable .txt or .cfg file, I agree with you on that.
But when it comes to settings like lives available, amount of items around the level etc, you should encrypt it (if you wish to be able to modify it say, dinamically according to player progress. If you already have a fixed value for what you want you just place it in the code and compile it).
Or don't you think professional games don't have encrypted configuration files reserved for the software exclusively?