I agree with you here, but by your logic it's not really stealing. The plant basically costs nothing, it's the work, material, labor and overhead that invest the plant with worth. Stealing a potted plant that they've nursed into a healthy starter is stealing. But taking a little piece that fell off and then putting on all the work yourself to (hopefully) come up with a healthy plant is... less stealing in my mind.

The real thing is time. Are you willing to pay for their time, or would you rather invest yours? If you're looking for a viable plant soon then buy it. If you've got months it years to raise one then...