Regarding the Intel comparison, you have no choice but to trust them, but by using Apple products, you are trusting Intel and Apple, which is worse than just trusting Intel.
may be
This is called faith
In this case I decided trust the open-source community more than Apple, since the incentives of people inspecting open-source code probably align better with my own interests than the incentives of Apple.
The incentives of any people are: earn enough money for a peaceful existence.
When Heartbleed happened, it turned out that only a handful of people in the entire world have the expertise to do a full audit of the OpenSSL code. And their work is ridiculously expensive. And the audit didn't happen until someone paid for it [1] (I'm not entirely sure it ever completed [2]).
People may actually have less incentives to inspect open-source code because there's always the question of life, money, time, work-life balance etc. etc.
[1] https://www.zdnet.com/article/ncc-group-to-audit-openssl-for...