Earlier quoted context omitted.
There are serious attempts at secure container runtimes (see gVisor) and runtimes that run container images in a real VM (see Firecracker). This meme that containers are inherently insecure just because Docker doesn't attempt to be a security product needs to die. Docker hasn't been the only player in the container runtime space for a long time.
Insecure is a very strong word, world has been running on Docker for sometime and it works fine and is not as insecure has you seem to think.
Thus, when people bring up "Docker is insecure" I try not to get down in the weeds arguing about the specifics, and instead point out alternative projects that are designed with security in mind. I find it's a much stronger counterargument.