I think it's perfectly ethical. I think it shows that you've grown talent-wise and realize the mistakes that were made. If a potential employer saw the errors he might think that you didn't know what you were doing. It's almost like having a typo in your resume, since your portfoliio is a part of your CV. If it really bothered you, you could always tell them about the changes you made in order to highlight how far you've come since then.

Besides, they're hiring the 2006 you, not the 2002 you.