Embarrassed by its cobbled-togetherness. Not in whether or not it works.
I would contend that if you have proven to yourself that your code works and are therefore capable of proving it to other folks (via e.g. solid testing), you should not be ashamed of the spit and glue.
It is research code, we all know what that looks like. But if, on the other hands you haven't proven to yourself it works, then it's definitely something to be ashamed of - scientifically speaking.
Most academics write code to just work. Not work well, or to be generalized, or to be efficient, just work. And while that’s absolutely fine, as your results being reproducible from the code is all that really matters, a lot of people don’t see it that way and will only see code slapped together haphazardly and dismiss you because of it.
Imagine if this reproducibility excuse were applied to experimental results and technique: we don't have be careful or explain in detail what we are doing, as reproducibility will take care of any errors. One consequence would be that, as the current state of knowledge became less certain, it would become less clear what to do next.
Publishing scientific papers that no one can re-implement does, and hugely so.
Therefore, not a very adequate comparison.
Especially in fields like physics there are many limits that you can derive analytically. Some times those are highly non-trivial.
I do appreciate papers that give you either a reference implementation or at least enough details on how it was done. I spent too many hours on papers that didn't trying to reproduce their claimed results...