What word would best suit this analogy?
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Drawback is the first word that comes to mind. Other possibilities listed by Wiktionary are disadvantage, hindrance, encumbrance, nuisance, obstacle, or detriment. (Listed more-or-less in decreasing order of relevance, at least in my opinion.)
I'm not sure exactly how benefit should relate to pro, but as pro and con are opposites, I would consider detriment to be appropriate.
Merriam-Webster also lists: disadvantage, drawback, encumbrance, hindrance, impediment, minus as antonyms for benefit.