I've been thinking of publishing graphic design instructional books and tutorials for non-designers. But I'm concerned that this could negatively impact my business. However, I really like paying it forward and enabling people do be self-sufficient. At the same time, I have to make a living.
I don't think you'd personally lose clients. What I've seen happen while working as a freelancer, was that regardless of how many resources were available for the amateur or non-designer, at least half of those who had began a project had then the need to consult with a professional after not being able to achieve exactly what they were aiming for.
Designing a piece is much more than putting together a graphic. It is, I believe, every decision you make before that. Why going for certain colors, or typographies, why this and not that layout.
Resources like the ones you mention were something I found really inspiring and useful when I was beginning to experiment with design. I owe most of those early years of self-instruction to professionals who offered some of their knowledge in this way. It was probably just a small portion of what they did for a living, but for me it was invaluable.
The impact on your business (or 'the world of design' as a whole, if you will!) will depend on how you present this materials. If you offer them in your personal website, along with your list of services, you might lose some potential clients. Were those clients going to call you, or would they have just kept going until they found a different site with templates? Not everyone wants to build their own stuff, some people prefer to just delegate. And I'm not so sure these two groups are that close to each other. So, in short, my answer: Nah, I don't think you'd lose clients.
I don't believe so. After all, chefs write cook books, craftsman (metal/wood workers) write instructions for their products. Paint by numbers is paint by numbers. It's really no different than designing and selling or providing templates. Sure you may be allowing some projects to be done without your services. However, they all end up looking the same.
If your client base is that niche that wants things "to look the same as everyone else" then you may very well do yourself more harm than good. But if you have a broader client-base with varying projects, I doubt it would really do much harm. You may not get those projects as much, but if they are small, relatively inconsequential projects, it may not be a problem.
Having a recipe is merely a roadmap. It does not inherently mean someone can read instructions and come up with something as well done as a professional. There's an inherent sense or "talent" which most professionals have that can't be detailed in any instructions.
I've had many a client who took one of my pieces to someone else and asked them to replicate the design. Having a visual guide in front of them often means they piece seems similar but is lacking something.