Why on earth would you send letters? These are all huge corporations with sizeable legal departments. They either know or they should, and most importantly, are paid to handle this. Moreover, you're not likely to be heard or understood by the first line of customer care there, even if this was something they weren't aware of (quite unlikely) but wished they were. It's a waste of time, and something even the biggest altruist would find hard to defend as a sensible effort.

Besides, Disney is perfectly capable of degrading their own brand.