Who do trademarks protect?

While your example is reasonable, and that may well have been part of the original intent of
trademarks, I think you are being too charitable to the big corporations and the "Intellectual
Monopoly" movement in general.

Generic drugs and store-brand food products are two counter examples. If they are identical
inside, why can't they be marketed under the trademarked brand name? Because the trademark
owner wants to keep the extra profit that comes with a higher price. I'm not saying that is
necessarily a bad thing--just that trademark protection (these days) benefits the holder more
than the consumer.

Of course with software it's even more clear. In the early Red Hat days, companies selling
*exactly* the same bits as RH were not allowed to use the RH brand name. Again, not
necessarily a bad law/rule, but to the benefit of the vendor, not the consumer.