If it were failing, you'd need to go and remove all the build steps that call the disabled build plan. The scenario that this issue was raised in is that a team wanted to temporarily not deploy to one datacenter, so they disabled the build plan for that datacenter.

Basically, if this failed build steps for disabled build plans, then you might as well just remove the build step instead of disabling the plan.

(to be honest I'd like to have maybe a "skipped" build target status so it's obvious nothing happened, but that feels like a larger change than this bug fix)

I think this scenario would be better handled with a "Skip" or "Pass" build step than treating disabled plans as automatic passes. That behavior seems very unintuitive to me.

You mean you'd rather have a build step you add to a build plan that skips the rest of the build targets?

I was also thinking we could allow build steps to be disabled from the UI, so people could just disable individual steps.