Full transparency - with lots of people having access - is desirable from society's point of view. Then, there are more eyes looking for flaws in the code - which makes is safer. Also, then, society can watch to ensure development is going along the right lines. This is likely to make the developers behave bettter, and having access to the code gives society the power to collectively protect itself aginst wrongdoers.

The most likely undesirable situation involves copyrighted/patented/secret server side machine intelligence sucking resources to benefit a minority at the expense of the rest of society. This is a closed-source scenario - and that isn't an accident. Being able to exploit others for your own benefit is one of the most common reasons for secrecy.

EMACS is a powerful tool - but we do not keep it secret because the mafia might use it to their own advantage. It is better all round that everyone has access, rather than just an elite. Both society and EMACS itself are better because of that strategy.

The idea that you can get security through obscurity is a common one - but it does not have a particularly-good history or reputation in IT.

The NSA is one of the more well-known examples of it being tried with some success. There we have a large organisation (many eyeballs inside mean diminishing returns from extra eyeballs) - and one with government backing. Despite this, the NSA often faces allegations of secretive, unethical behaviour.