Your missing the point. It's all about the perceptions of future adopters. It doesn't matter whether governments can technically take down the bitcoin network/protocol... they can massively inflate the perceived risks of future adopters.
When push comes to shove, the layman sees many alternatives to what bitcoin provides (especially since the vast majority only see bitcoin in terms of fiat and little more). If governments want to hurt bitcoin, they can censor, make transactions illegal (or cast them in a legally questionable light such that users will seek safer alternatives), use banks to target exchanges, businesses and even users -- seizing assets and crippling operations along the way. The negative press any such actions would bring would blow out of the water any and all fundamentally bullish indicators.
They can stop digital fiat exchange in their country. They can't stop the rest of the world and they can't stop cash transactions.