First of all, I never said "safe". Just that after working for a while, people would tend to not worry about it.
That's kind of true for a highly leveraged debt based system too. It took several years post-2008, but most now ignore systemic risks, or deny they even exist at all.
So I agree with you that many will behave that way in practice, but I also believe there is a role to play for systems built on a stronger foundation.
if the best argument against Zerocoin adoption vs Monero adoption in the privacy-coin niche is that ZC uses new crypto
That is a massive issue though (even if many people may ignore it). In cryptography the only thing that makes most real systems secure is that they have been around for a long time and vulnerabilities have been either identified and fixed or unable to be found. It is essentially impossible for new crypto to be usefully secure. 10 years is a widely recognized rule-of-thumb aging period. The key components of zerocash are far newer than that.
This is not just an issue of privacy either. If the system breaks there could be huge or total monetary losses.
Understood, but you have to view that risk in the context of the rest of the risks in any crypto-coin system. A break of the underlying crypto seems down the list relative to other (probably more likely) failure scenarios that can be equally catastrophic from an investment standpoint.