Hi!
Ask yourself what it is about.. It is about the Wikimania talks. What was done is removing all the Wikimania talks without any discussion.
I wonder whether Wikidata is really the best platform to host Wikimania talks and information about it. While I have no doubt these are excellent talks of great interest to Wiki community, their notability in the larger world is a more difficult question. Specifically, would we create an item for every talk even for a major conference (not considering copyright etc. questions now)? We have a lot of conferences with much wider attendance than Wikimania happening each year.
Now, Wikimania is of course special - for Wiki movement. And having *some* repository for this content and knowledge would be completely appropriate. However, is that repository Wikidata - as purported to be repository of knowledge of general public interest? I am much less sure of it. Unless we take the wider mission of accepting data about talks on any conference of note - which may be possible, but I'm not sure whether it should be done... If yes, then of course clear policy statement to that effect may be helpful - so people who are not sure about it like me would know what the community consensus has arrived to.