Do Stack Exchange sites allow to include copyright/license in code snippets?

Question

Suppose we see an answer with a code snippet like this:

// Copyright (c) 2017, <some guy's name and email>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

// <code...>
// <code...>
// <more code...>

Is this allowed (or if yes - is it a proper practice?) in code snippets on Stack Exchange sites? Or we should require authors to remove this stuff from answers?

ADDITIONAL QUESTION: Essentially all comments to this question say that the license above is more permissive than the SO license.
Please explain, why?
For instance, the above license requires to include the copyright/permissive note and the name of author to all copies of my code.

UPDATE 1 (answering to Servy's comment): The copyright notice shows the person that posted the content.

Answer 1

While there is nothing that prohibits content here being distributed under more than one license, all content here is distributed under our license.

If they'd like to distribute things under alternate licenses in the process of creating it here, they should to go publish it somewhere else under that license - we're not a hub for creating content under a bunch of different licenses. We've encouraged users to add disclaimers like this in their profile before if they want all of their contributions to be sub-licensed under a more permissive license, but it frankly doesn't belong in the post's body and only takes up more space on the page.

If that text is required to be there due to some other license the user isn't authorized to override, then the content doesn't belong here. By publishing it here, the content must be eligible to be re-licensed under our CC license. Requiring a specific block of text at the front of the code is against the terms of our license and thus distributing it under our license is not allowed. That's not to say it should be deleted altogether. Users and moderators are not copyright enforcers and should not be engaging in deletion of content that may or may not violate someone's copyright. That is what the DMCA process exists for and if the user who owns it would like the content removed, they can file a proper complaint and have it removed.

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In simple terms: Our network's license essentially allows a user to completely ignore that block of text, because it's not required to be there under the license terms. Therefore, it is useless information to a lot of our site's visitors. While there is no hard rule that says those blocks of text can't exist, we would not defend an author attempting to force it into their posts after it was removed, and in the event of an edit war, would lock the post in a state without the additional license to resolve the dispute.