I dislike default dynamic scoping because it seems like a bad idea to me. The fact that other Lisps already have it seems pretty irrelevant, except insofar that it gives us a chance to try out dynamic scope and see what it's like.
In other words: I think old ideas are fine, and new ideas are fine. Ideas should stand on their own merits. The only difference between an old idea and a new idea, is that the old idea has been tested somewhat, so we can have a better idea of whether it's a good idea or not.