Making a kernel as a hobby doesn't put anyone in danger. And using a kernel someone else wrote as a hobby doesn't tend to put anyone in danger, either, because it's very clear when a kernel was written as a hobby (mostly because you can [almost] never run common commercial software on such kernels — a hobbyist kernel with Illumos-like "branded zones" supporting Windows or Linux software would be a very dangerous beast, if someone wrapped it up into a black box.)
To contrast, writing crypto as a hobbyist isn't dangerous, but using someone else's bad crypto can be dangerous indeed—because it's almost never clear that the crypto within the software you're using was written by a hobbyist.
People can learn crypto all they like. In private, sharing their learning with peers and/or mentors. But their "homework projects" should never be posted on the public Internet where they could be found by people looking for professional solutions, any more than a chemistry student's homework project of devising a work-up for making non-volatile explosives with volatile intermediaries should be posted on the public Internet where it might be treated as a safe, well-known procedure for doing so.
You don't need your crypto to be wrong for your software to be compromisable and dangerous to users. People use random packages and libraries all the time, and it's thought a best practice to not write things, to reuse random stranger's code instead. Yet when we talk about crypto, people jump to their guns. When we talk about package consumption and management, people are way more chill about it. In that sense crypto _is_ put on a pedestal: it's just one among many parts that can make a system unsecure. I guess it's worst in the sense that it gives an illusion of security. Yet for all practical purpose, it's just as likely to be wrong as any other part of the system.
To contrast, writing crypto as a hobbyist isn't dangerous, but using someone else's bad crypto can be dangerous indeed—because it's almost never clear that the crypto within the software you're using was written by a hobbyist.
People can learn crypto all they like. In private, sharing their learning with peers and/or mentors. But their "homework projects" should never be posted on the public Internet where they could be found by people looking for professional solutions, any more than a chemistry student's homework project of devising a work-up for making non-volatile explosives with volatile intermediaries should be posted on the public Internet where it might be treated as a safe, well-known procedure for doing so.