This is why I didn't say it made the investment risk free, I said being capital intensive does not make something (inherently) risky. There is no such thing as an investment without risk, but how risky it is is largely orthogonal to how capital intensive it is, and the above was talking about the latter so using the term "risk" for that half is not a great correction.
Expensive is a better fit than capital intensive, because there are massive ongoing costs to actually perform the attack, electricity for one.
If you want to understand the risks for a project, pretend you are at arms length and are being asked to fund the project 100% up-front. You'll find a huge list of risks very soon.