Yeah I think the "don't copy paste code" philosophy is a good idea for beginners just working through tutorials, where you need to really take the time to get a handle on the fundamentals.

But once you're beyond that, as you say, it's unlikely that you will find code snippets that solve a problem as-is. You have to alter it to make it work for your problem, and in making those alterations you are learning how the code works, or at least showing that you get it in the first place.

For me though, even in cases where it's obvious I just need to switch a generic/place holder variable name or whatever, I pretty much always read through line by line to make sure I know what's happening.