I think questions about uninstalling software from Ubuntu should use the
software-uninstall tag. If there are many questions about uninstalling Ubuntu, then there should be a tag for that, too. I don't think there should be a
uninstall tag, though since it has over two thousand questions, a mass retagging effort should start with a meta post to ask what people think should be done, especially considering that the
uninstall tag is currently an order of magnitude less used.