To be fair, we only know of this one. There may well be other open source backdoors floating around with no detection. Was heartbleed really an accident?
True. And the “given enough eyeballs, all bugs are shallow” is a neat sounding thing from the past when the amount of code lines was not as much as now. Sometimes it is scary to see how long a vulnerability in the Linux kernel had been there for years, “waiting” to be exploited.
Still far better than a proprietary kernel made by a tech corp, carried hardly changed from release to release, even fewer people maintain, and if they do they might well be adding a backdoor themselves for their government agency friends.