You use software written by other developers. Do they have malware? Do they know they can trust their compilers to not insert backdoors into the code they write? Sure, you can trust people. But can you trust their accounts and their computers? Did they buy a computer in a random store? Did they get it shipped? Did it get tampered with in transit?
Think of all the important software projects in the world that people trust and rely on. How many of them are just being developed by people using run-of-the-mill computers with no special supply chain security? How many people just install tools without doing checksum verifications? How many people click through certificate warnings? How many developers enable javascript?
So you could say ``use X software because it makes you secure'' but are the people who make said software secure themselves?