Is this appropriate?

So I'm sat in my Sixth Form history lesson, we're doing Weimar and what not. This history teacher is trying to explain why an electoral system of proportional representation is impractical. Not everyone's getting it, so she dumbs it down to a ridiculous degree and just says "Well, if we had proportional representation in the UK today, the BNP, which a fascist, right wing party would have a seat in parliament." First off, this explains precisely nothing. Secondly, is it really a teacher's place to imbue their lesson with such blatant personal opinion? I'm pretty sure the whole cl, including myself, find the party despicable but that cannot be an argument against a system. Surprisingly though, the majority felt they understood it at this point.