I would think since mousesavers recommends them, that they are fine, I am unsure why skiingfast thinks they are unethical, so I cannot respond to that.
The ones that are unethical are those on ebay/craigslist that buy unused days on used multiday passes to resale the remaining days and/or upgrade the passes. Now that Disney is printing names on multi-day tickets, I would imagine that this practice will be reduced.
Places like ARES that are officially authorized by Disney to sell tickets are fine.