I believe you are too preoccupied with USD. The feedback loop of (lower USD price -> less users -> even lower price) has never before held true with Bitcoin, and I have no reason to believe it would now.
What about 2011?
In between 7-11/2011, the number of non-dust addresses grew by 30%.
Even if we assume that there is such a negative feedback loop, 2011 was a proof that it was reversed and did not self-immolate.
So far we have one vicious bear market that was reversed, and 5 years of gains. My theory is that Bitcoin has a self-reinforcing positive loop which will eventually consume fiat totally, and all the bear markets are temporary. If you say otherwise, the burden of proof is on you because such an assertion is not supported by neither history nor reason.