If you believe that "don't roll your own crypto" is some kind of absurd mantra the security industry uses to keep us in business, I recommend that you roll your own crypto, and keep us in business.
I would compare it to a writer's inability to spot typos in something they wrote themselves. Probably, if the same algorithm was written by someone else, they could tear it apart easily.
I do not have concerns with the mantra itself just it's usage and the entitlement that often comes along with using it. The top answer on this Stack Exchange question is a good example of what I believe to be proper usage of the mantra.
http://security.stackexchange.com/questions/18197/why-should...
How far should we take that maxim? It implies that no one should ever attempt this, but that leads to nothing new (unless you are first recognised as a crypto guru -- but how could you become one?).
I think it's worth drawing a distinction between the algos/maths and attempts at implementations. Otherwise we wouldn't have things like OCaml-TLS and others.
Implementations are even more sensitive to tiny bugs with huge consequences than algorithms. It's fine for people to write their own implementations if they're never used, but anything that will be used needs a large number of experts and a large amount of time before it should be trusted.
"Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can't break."
https://www.schneier.com/blog/archives/2011/04/schneiers_law...