The author’s conclusion is based on the mistaken assumption that the majority of the students disapprove of the union effort. It’s not based on the premise that unionization agrees with a long-standing practice.

The author is just arguing that because students disapprove of unionizing, they shouldn’t unionize. He doesn’t need to address all possible explanations for why the students might disapprove of unionizing.

Instead, the author assumes that simply because a majority of the students are unaware of the unionizing attempt, those students must also disapprove of the attempt.

The author concludes that the students shouldn’t unionize because most students disapprove of unionizing. It doesn’t matter whether there are other reasons for unionizing.

The author assumes that the majority of students actively disapprove of the union effort simply because the majority of students are unaware of it. But just because these students merely lack approval for the effort doesn’t mean that they disapprove.