They didn't enter the first pubic war with the intention of conquering Sicily, they didn't enter the First Roman Syrian War with the intention of conquering Asia, and they didn't intervene in Greece initially with the intent to conquer it. There are a few instances where they did have a set goal-conquering Ciscalpine Gaul to protect from Gallic incursions, or entering into war with the Samnites to secure Campania, but this was the exception rather than the rule.
This is what their historians would have us to believe, at least. It reflects the Roman ideology of just war, but that ideology, regardless of how sincerely believed by the people involved, covered the Imperialist results very well: nobody forced the Romans to conquer the places they happened to conquer (and allegedly did not want to), except that they consistently did. One sees a pattern there. Not an Imperialist grand strategy in the sense Alexander had one, yes, but clearly a consistent inner push to expansion, which ended up to be inbuilt in the mentality and practice of the Late Republic and (to a lesser estent) Early Empire. They did not officially start expansionist wars, from their perspective, but this hardly means that their wars, which ended in conquest where truly defensive (some were, but are probably exceptional).