That is not a fair assertion, as source confidentiality to limit wide-spread computerized and manual inspection of backend code to find flaws is just one of man

That is not a fair assertion, as source confidentiality to limit wide-spread computerized and manual inspection of backend code to find flaws is just one of many tools to mitigate attacks. For instance, in this case a group with sufficient security research skills politically opposed to some of the gab users seem to have utilized the source-code to find a vulnerability the Gab team had not discovered yet.