There are plenty of reasons to be concerned about this kind of thing, but the basic premise of this type of revenue generation is sound. What they are trying to do is move toward a system where the users of the roadway system incur a cost that is more directly tied to the type of roads they use, the times they use them, etc. This is exactly what is needed to alleviate the kind of congestion that has become a recurring problem in every major U.S. city.
Regardless of the economic soundness of it, agreeing to it amounts to sacrificing our principles for expediency.
As a side note, I doubt it will replace gas taxes in the end, we'll have both.