I've looked but can't find the rationale behind that law. I know the real reason was to keep drug prices high but how was this sold to the American people?
The doesn't really answer my question and from what I can tell the measure was rather bipartisan.
The fear is the "bargaining power" that will be used is "give it to us or we invalidate your patent." And the fear is valid, because that's how most other countries' governments negotiate.