I mean, you know they aren't going to have adequate content moderation because they ALREADY don't. Lack of moderation is the #1, #2, and #3 best reasons to defederate.
Wanting to see proof before taking positive action is valid and sensible. But you can't pretend it isn't something you can already make reasonable inferences about. This is not a new unknown and pretending it is is ridiculous.
Email servers do not automatically feed content into and pull content out of your system. They only send and deliver to specific people at specific addresses. Federation is a firehose. You can close the hydrant before or after it gets hooked up to city water, but at the end of the day only people that chose to do things the sensible way will have dry socks and no water damage.