Afro Wigs Offensive?

Halloween is approaching and I've been reading many blog post on racist Halloween costumes. Some costumes are obvious in their offensiveness: All "sexy" professions (because women can't just be professionals), caricatures of traditional costumes of ethnic groups (Native Americans, Asians) but are afro wigs as part of Halloween costumes offensive?

Before I wrote this post, I googled afro wig and was surprised that ANY curly wig is referred to as an afro. The wigs were red, pink and blue, isn't that just a curly wig or even a novelty wig. I don't think these have any relation to my hair or hair texture.

My next problem is how they are advertised:


What's with the silly faces? Is this a hair style that is inherently comedic?

And last but not least, why would a colorless person NEED an afro wig for a costume? If they are invoking the 1970's they can just do straight hairstyles from that era. If they are portraying a person of color isn't wearing and afro wig just as bad as blackface?