While it may be considered a simple breach of etiquette, maintaining and forging relationships is a survival skill that is very much needed in the group's current situation. However, what they did has the very real potential of driving a permanent wedge between Hershel's clan and their group (this is something I have a feeling Shane understands).

This means the group now faces the very real likelihood of having to head back out on the road. In other words, people will likely die as a direct result of Shane's decision. This makes the decision to clear out the barn a poor survival decision in my books.

Of course, from a story perspective, this is good because people were getting bored of the farm. We don't want the group to be safe, we want action and drama. But from a survival perspective boring is okay.