That's the typical reaction I get when I try to explain that English has no future tense. Perhaps the reasoning is similar to that which lead Ann-Marie MacDonald to write that "the present tense will reign"; People tend to conflate tense and time.
But it's not just this misunderstanding. A future tense seems to be some kind of mark of pride. Being told that your language doesn't have one often brings out Chauvinistic zeal in everyone from English teachers to students from Japan, Korea, Turkey, Finland, or Arab-speaking countries. "Of course we have a future tense," they say. In fact, the only group of students I've come across who have no problem with the idea seems to be Chinese students, who actually tend to be rather proud that Chinese has no tenses at all. (Of course, many languages, such as Spanish, do have a future tense.)
But getting back to English, ESL teachers and our materials are almost unanimous in their agreement that will and (be) going to are (is?) the future tense, despite decades of linguistic analysis telling them otherwise. Yet, it makes far more sense to teach will as one of the nine modals rather than teaching modals and then treating will separately as a tense. Similarly, there's nothing special about the going to idiom, which acts almost exactly the same as planning to, hoping to, intending to, etc. From there, it's a short hop, skip, and a jump to the idea that the present tense is often used to talk about future events, and that the past tense has meanings other than past time.
Perhaps someday there will be a pedagogic ESL grammar series with no future-tense nonsense.