I think you may be setting up a bit of a straw man argument here:
Coding limits your design thinking because you’ll only be creative within the bounds of your development skills.
The argument as I understand it (and as I myself have framed it) isn’t that coding limits your creativity; it’s that it may constrain your creative decision-making. I.e., you’re no less creative, but you may opt for a less creative or adventurous option in some (or many) situations.
For example, imagine you’re under a tight deadline on a challenging project. You’ve told your client or employer you can do it all, design to development. During the design phase, however, you have an incredibly creative idea (because of course you’re capable of such things!), but you quickly realize it’s well beyond your coding skills. I think the risk that you’ll constrain your design thinking is a real one—and one I’ve experienced myself when I used to code.
I agree with your primary assertion, however, that this is not a zero sum game, and that those who frame it as such are mistaken. If you want to be a designer who codes, excellent. You’ll be on a slightly different trajectory than one who doesn’t, but neither is inherently better or worse, market demands aside.
But if I may insert my own straw man for a moment: I feel the argument that learning to code can’t possibly hurt your work as a UX’er or designer is also a tad intellectually dishonest. As Jared Spool tweeted to me yesterday:
Do chefs limit themselves when they learn a new cuisine?
I’d respond that yes, maybe they do. I know that we live in the age when we like to believe we can Have It All (and of course we deserve it, too). But reality doesn’t work that way. The chef who wants to be outstanding at, say, French cuisine should probably spend most of her time learning about and preparing French food. If she tries to split her time 50/50 between French and Chinese, she may not be as good at French cuisine as she wants. If she decides to do French, Chinese and Middle Eastern, more so. If she’s going for fusion, great, but to be a master class French chef probably requires an explicit focus on French cuisine.
And anyway, it’s kind of a false dichotomy set up by Spool because cuisines share a greater lingua franca than design and programming. E.g., learning how to prepare Chinese flat noodles probably has more carryover to French cuisine than learning how to vertically center an element in CSS does to creating meaningful user testing scenarios or writing microcopy.
So, yes, I do think it’s a tad disingenuous to suggest that trying to be a unicorn doesn’t come with some potential tradeoffs and risks, as well as some benefits. In other words, the zero sum game argument cuts both ways.
Disclosure: Aaron and I are not only good friends, but we are also the two UX’ers at TED.