More generally, people don't even agree what education is for. It could be:

• preparing people for their future jobs;
• preserving the knowledge of humankind, maintaining culture;
• improving people mentally, creating better neighbors and citizen.

Generally, all these goals are considered good, but sometimes they are in conflict, if you try to optimize for one of them too much. For example the first rule, in extreme, would require learning only details related to one's future job, nothing more; but students could learn more details, and have more practice when they finish the school. The second rule, in extreme, would require teaching everyone everything. The third rule requires a value judgement what makes a person good citizen, and in extreme, it would require focusing on those skills and ignoring everything else.

In many discussions about education, one of these ideas is assumed implicitly, and then there is a suggestion how to get closer to this goal... usually at the expense of the remaining goals, which is why other people protest against the suggestion.