Because it formalizes thought and encourages people to use templates rather than actually thinking about it themselves. If you're "solving problems" by always referring to your sheet of "problem solving approaches", then you're doing it wrong. You might still be successful in solving a problem, but you've effectively turned yourself into a robot.
Anyone operating in a template-driven manner is not reasoning by first principles. I'm not sure what legs your argument has, we might as well say that speaking an existing language like English, French, or German makes us robots by forcing us to communicate within a well-defined and rigorous communication structure.
The fallacy of an individual with regards to reasoning is not a function of the fact that methods of reasoning are identified - they are failures of the individual to effectively apply their own creativity. Don't blame the linguistic constructs.
"Anyone operating in a template-driven manner is not reasoning by first principles."
I'm saying that when you want to solve a problem, you don't use a checklist of which "reasoning from first principles" is an item. "reasoning from first principles" would be the template. It's an approach that someone spoonfed you. There is no contradiction here because we're speaking about the type of approach, not the particular sequence of steps you use to arrive at the solution. Of course you can be creative with these steps once you know the type of approach you're taking.
"I'm not sure what legs your argument has, we might as well say that speaking an existing language like English, French, or German makes us robots by forcing us to communicate within a well-defined and rigorous communication structure."
Natural language is well-defined and rigorous? That's not true.
"The fallacy of an individual with regards to reasoning is not a function of the fact that methods of reasoning are identified"
I don't care that it's labeled, per se, as long as people are discouraged to act like I mentioned. If the act of identifying and labeling thought patterns promotes laziness, then I am justified in being against it. But anyway, that's an empirical claim and you haven't provided any real reason for why you think it's false.
