You have been listening to extremists and politicians. Inversion does not change their tax status on U.S. operations. They continue to pay the same taxes. They just won't pay the U.S. for earnings on their European acquisition. Boots does their business in mostly in Europe, and a little in Asia. Why should Walgreens pay taxes to the U.S. for the business done overseas, which will be taxed in Switzerland?
I couldn't agree more how wrong people are about tax inversions. US is the ONLY country in the world that taxes it's citizens on world wide income. If a person lives and works abroad, they still have to pay US taxes. You hear about people renouncing their citizenship because of that and you will hear about companies doing the same.