Besides, making the code public will also help hackers, it will be simply a toss of a coin, who will find the flaw first, a good guy or a bad guy.
That's absolutely NOT how open source code works. It's actually the safest code
because it is picked apart by the community to ensure that it is safe
before it is released. When has Bitcoin been hacked? Closed code is notorious for having security issues & vulnerabilities, plus you have no idea what's in that code of course.
The bitcoin code has proven to have flaws a lot of times and a lot of times new versions fixed have been rushed.
And this is exactly how open source code works, you let people know your code, you let everyone know how the code is written and how it works. Just because 20 guys said: ok this version is ok it doesn't mean it is.
And the supreme argument why it is not better like that is that nobody is doing!!!