In the other, no act is performed (simple abstinence during fertile times) so there IS no act, therefore the practice is morally neutral.
I spend money every day: to support my family, pay my taxes, give to charities, etc. Suppose in the future, I choose to abstain from spending on any charity. Is this action morally neutral because no act is performed?
Still rolling around a rebuttal to an abstract analogy that compares sex and vomiting... See the first paragraph of my first comment.
Instead, I think I'll log off, go home, light a fire and enjoy my family.
It takes moral blinders to ignore simple Natural Law.