I don't think that is what he is saying. I think the key sentence is the first one, not the last in the quote: the courts should let those who want to market new technologies carry the burden of persuasion that a new exception to the broad rights enacted by Congress should be established.
In other words, the burden rests with the one exploiting a new technology that invades someone's copyright. He is not saying that the burden of legality rests on the new entrant, just that the burden is there when it requires an exception to someone else's already-legislated rights.
In other words, the burden rests with the one exploiting a new technology that invades someone's copyright. He is not saying that the burden of legality rests on the new entrant, just that the burden is there when it requires an exception to someone else's already-legislated rights.