Here’s why your analogy, or whatever you call it, doesn’t work:
If you take a hunger-canceling pill (contracepted intercourse) when a dinner (natural intercourse) is available to you, you are engaging in self destructive behavior, which is immoral.
If you use contraception (sugar pill) when you are unable to conceive anyway (no dinner), it is no big deal, other than it is stupid.
The issue is using artificial sweetener in place of sugar, in order to avoid undesirable physiological results of consuming the latter. Please try to keep up with the class.