Is fallacious reasoning used to get an argument going?

It does beg the question, but not in a way that most people might think. The part that begs the question is the claim that it is used extensively in packaging food products. This seems like a fair claim and one that is most likely true so it would be unreasonable to call fallacy or reject on those grounds. The "If plastic is harmful..." may or may not beg the question. Technically, it doesn't. It is presenting a hypothetical to which the person is asked to entertain assuming the antecedent is true (e.g., "if pigs fly then would our homes be covered in pig poop?"). More informally, however, people can smuggle claims in under the guise of a hypothetical. This would be more of a problem for the person reading the question and interpreting the hypothetical as a fact (in this case, that plastic is harmful). The best strategy to answer something like this might be to make it clear up front that you are treating this question as a hypothetical and do not necessarily accept that plastics are indeed harmful.