I think I have been guilty of at least one of these 'crimes'. Perhaps describing them might reduce your stress levels because in each case I believe they were honourable.
I have, once, added a whole family to my tree that was, at that time, completely unconnected.
I collected the data from census so it was all public domain.
I chose to do this to try to find the connection of this family to my tree. I had good reason to believe that they were connected because their surname appeared as middle names in FOUR generations of my tree.
I did have several contacts, one of them helped me connect them up to mine and they are all there now.
I have just tipped over the 2000 people in my tree. I have been doing this for less than a year. I know almost nothing about most of these people.
When I first started growing my tree I made a conscious decision to allow this to happen in the early stages. That stage is now almost over. I am now able to study them, explore them, make them my friends. I believe I made the right decision.
That's the end of my confession but I would like to touch on one other point people have raised here.
I hold four different copies of my tree, one on my pc at home and one on each of Ancestry, GR and Tribal Pages. I find this easy to manage and control although the Ancestry tree is the most difficult.
The only way I can achieve this is through using Gedcom files. Please do not throw the baby out with the bathwater. Gedcom files are incredibly useful when you want your tree on public view.
Carefully used, Gedcom files can be great timesavers. If, for example, you hold a tree on GR, you can download it from there, upload it to Ancestry and it all looks about the same.
Happy hunting.
Paul