This is hard to defend, guys.
It is literally the-simplest-thing-not-to-fuck-up. Nobody's asking you not to have security vulnerabilities. In fact: nobody's even asking you to fix vulnerabilities. We just need a reliable way to communicate with you about them.
If you're selling accounts on a web app, you need:
* A security page * With a PGP key * And an email contact * of someone who will write back * who knows what a security vulnerability is * and who will write back quickly.
That's it. Do that, and you're not a punch line. If someone dumps zero-day about you onto Twitter, you're already two steps ahead in the PR war, because you had a reasonable process, and the researcher ignored it.
Bonus points --- things that are trivial to do, but that nobody's even asking you to do:
* You can assign special issue numbers to vulnerabilities, to make the researcher feel like an XSS disclosure isn't the same thing as a bug in your online help.
* You can thank researchers privately, and let them know that you'd really like them to keep disclosing thing to you --- you could even give them (wait for it) a phone number.
* You can do what every vendor with a real security team does, and keep a public web page thanking people who have discreetly disclosed vulnerabilities to you.