The people who take this advice are people who have respect for the difficulty of things like crypto and should be the ones implementing it, or at least on-ramped into learning how to do so.

The sorts of people who ship bad crypto because they don't bother to learn anything about the field are going to ignore this advice.

So I think as a strategy for fighting bad crypto it's neutral or maybe even net-negative by discouraging the right people from learning crypto and having no effect on overconfident fools.

Someone (Bruce Schneier?) said that the best way to get into actually inventing/implementing crypto is to first get handy inventing attacks / hacking into other algorithms and tools.