[Maui Greenstone]

If you are trying to copy to better understand technique without plans to sell your copies that is totally acceptable. When I teach classes I want my students to pick up the technique and make it their own and if this means copying the design I've taught several times to better understand the technique then I'm totally cool with that. It's when they directly copy a design and put it into their production line and sell my designs that I actually take offense. Technique is for everyone, designs are an individuals intellectual property.
That being said. I believe when you purchase a tutorial it goes towards purchasing a design, kind of like purchasing a shirt pattern it is meant to be reproduced with variations(maybe the writers should disclaim wether it gives you rights to the design or just the technique) tutorials are no replacement for an actual workshop in terms of technical understanding of what the glass is doing whole executing a particular technique.
I am a firm believer in spreading the wealth of glass knowledge as far as it can reach, but I also believe that individualism and creativity in design is also essential.

In short it's ok to copy to learn, just don't profit from your replication. Take what you've learned and use it to round out your individual design pallet.