That's one way to look at it. On the other hand, when a format presents useful, but potentially dangerous characteristics (eg, XML entities expansion), it is entirely sensible to offer a way to not take them into account.

Quite fair. Depends on what kind of tradeoff you're looking for: this personally makes me search for a new format. It's reasonable to make a different choice.

I don't even think that's fair. What happens when everyone implements their own pet subset of a standard?

It's not an hypothetical future, you can often disable dangerous features in XML parsers. It seems sensible to me to do the same with YAML parsers.