This seems like an odd reason to exclude something. I mean, there are folks asking questions about plot points from folks who aren't the writers, and even the creation of anime/manga being answered by folks who are not involved in it... Even though you would hope to attract experts in each topic, at this point there will naturally be a lot of questions that either can't be answered, or must be answered by someone who is not an expert in the topic - hopefully by drawing on information provided by someone who is.
Now, I tend to agree that questions asking for legal advice should be off-topic, not because they would put answerers in danger but because they're not about anime or manga.
But the question you use as an example isn't asking for legal advice. It's asking for help understanding certain policies within the anime community which appear to be blamed on copyright law.
Focusing on the legal aspect here seems to be missing the point. Are anime conventions on-topic? Are anime music videos on-topic? These are the more important questions, and seem to fall in line with many other discussions on the topicality of anime / otaku-related culture here.