As already said, a wagging tail can mean contentment. Some cats show their happiness by wagging their tail. When they are intently watching something they are "hunting" their tail will wag a little more aggressively. If you are holding your cat or petting her and she starts lashing her tail (a very strong wag) then it would be a good idea to stop doing what you are doing or put her down gently and leave her alone till she settles.
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!