When I get tired of my video host or get locked out of my account, I should be able to download all of my own videos to put them on another host, regardless of whether the old host chooses to make that easy.
Journalists should be able to download every video of a politician making a false statement so they can play it back in a year when the evidence of that lie becomes better established.
Works by US Government entities like NASA are in the public domain. Anybody should be able to do what they like with them.
These things are distributed on the same services as anything else. A download tool can't evaluate the copyright status of a work or make a fair use determination. Prohibiting the tool is prohibiting all of the uses that should be allowed.