You work with publishers, though, and they may disapprove of this method as a hack. I don't consider it unethical myself, though, as long as you use only one copy of the book at a time and don't profit from selling multiple copies. Also, according to what I've read on the net forums, using just one copy hasn't been prosecuted in the United States.
I don't recommend this method, though. The Epubor software that will remove the DRM costs $39. For a little bit more, you can use a method without the drawback of doubts about its legitimacy. Also, though the Epubor site passed a malware-scanning test that I run in my browser, the downloads could contain bundleware, not necessarily viruses but annoying. (When downloading freeware or shareware, I avoid the default installation, choose the advanced one, and uncheck everything but what I'm sure I need.)