If you have to argue this position, you should focus on the impact that eating has on other students in the class and on the physical environment of the classroom.
You should talk about how a student who is eating in class can distract other students. The student's food might smell strongly and either bother other students or make them hungry too. A student might eat something noisy like potato chips and distract the class in that way.
Also, students who eat might spill their food. This could stain the carpets in the room. If there are no carpets, it would at least cause disruption because someone would need to clean up the spill, thus disrupting class.