Well, the writing-part isn't the bad part about duplicated code. It's the maintaining of it. In particular, if you duplicate logic, it happens all too quickly that you make modifications to one, but not the other, or you make differing modifications to both.

Eventually, you'll end up with two wildly different versions, where you won't know why certain changes were made and not applied to the other version. Similarly, if you do need to make a similar change to both, you might now need to implement it two times.

I guess, I do agree that it isn't *always* worth it, but in my experience, it is far more often worth it than one might think.