I think that's pretty clearly not the point. As someone who has worked with legacy scientific code written in Fortran, the copying is not the issue, it's blindly copying code that was written 50 years ago, probably by a graduate student, and not reviewed or revised in any way since. As the parent comment points out, if everyone reuses that code, the same errors propagate. It's not the type of reuse that comes with a nice GitHub repo and an established mechanism for reporting and fixing bugs.

In my case, one of the Fortran files essential to my group's research has 11 (!) versions with only filenames like file.f.goodworking (that's literally one of the extensions) to differentiate them and no version control or history.

I don't think this reflects the OP's concern: It's not that code-reuse is bad in and of itself, it's that the code being reused is being reused without maintenance or review.

Good point. For example, I'm sure no trained professional would ever copy code from StackOverflow.

This gave me both a good groan and chuckle.

You're pointing out a place where I think many software engineers are either untrained, unprofessional, or both. There's already a large body of discourse around the problems that come from these practices—licensing violations, security breaches, and stupendously dumb bugs.

Professional rigor is a thing I wish our industry had more of, but in practice you don't see much rigor outside of safety critical applications because there is rarely incentive for it.

If we reuse code, we risk missing a potential time investment!