"Wary" might be the wrong word. Students should always be skeptical of information presented to them. It's part of the critical thinking process. If a person is explaining politics in terms of political culture, they would fall into the realm of 99% of all people who might try to explain it. True scholars with a knack for explanation and an expert command of the topic can successfully pull it off most of the time. If by founded skepticism the student finds the explainer to be at fault through lies and/or half-truths, then the student would have reason henceforth to be "wary" of the explainer. However, most of those who provide explanations, i.e. teachers, do not fall into this category. They are likely biased, as everyone is on almost any given subject, and are likely just faithfully presenting information through their prism. This is why all arguments are evaluated based on their merit or lack of it. The idea is to keep an open mind then evaluate the information.
Explaining politics in terms of political culture is like explaining ham sandwich in terms of ham sandwich. It's pointless. I think the answer would be because that person disregards philosophy underlying politics - ie morality, religion, utility, liberty - which are supposed to construct politics