A competent programmer borrowing code would likely factor it in in a way that won't present maintenance burden later on, and first of all would know when borrowing is appropriate. An incompetent programmer may produce problematic code even regardless of whether it's borrowed or original.

(Though I'd agree that incompetent programmer borrowing chunks of code from different sources without thinking is ‘worse’ than same programmer just writing bad code by himself—more predictability in the latter case.)

In my case, I regularly see borrowed code in projects that I maintain. As long as it's contained in an isolated module, documented (unless it's short and obvious) and used appropriately, I don't see a problem.

Interestingly, front-end code I work on seems to suffer from much worse-quality borrowing—it's like Python people lose all their discipline once they turn to JavaScript.