We are not as bad as the United States of Idiots' dreadful educational system where only 31% of graduates can be classed as prose literate!!!! But we are getting there - and the UK system has dumbed down a lot in the last 20 years.
Thus, one cannot trust and believe anyone's qualifications any more. I certainly don't.
By your account, we are all doomed. I don't think I want to subscribe to that point of view.
Now, I assume that, when you say "dumb down", you are not referring to the field of science, technology, mathematics, medicine and the like. Because, if you are referring to these subjects, then we are, certainly, headed for a dark era. So, I believe that you are referring to the English language. If this is the case, I still don't see it as "dumbing down"; but, rather, evolving...
English, like most languages, is evolving. It may not be the English you know, but certainly, it is the English that most people recognize. For me, it is more important that it is recognizable to most. You need this aspect to make the message clear. For, isn't that what language is? A vessel to deliver our messages?
We cannot always contemplate on the negative. Whether we like it or not, America has contributed greatly to the evolution and the distribution of the English language. I believe that "evolution" is always a positive event. Of course, change always comes with contradiction (just as you have been doing in this forum); however, it doesn't mean that it is "dumbing down".
Perhaps there is no factual basis for any of the arguments presented since they are merely opinions to begin with. If this is so, then there is actually no argument.