not in the US, at least. if something is not subject to copyright, it's public domain. public domain stuff can be included in an otherwise-copyrighted work, including work covered by the GPL, without otherwise affecting the license. the GPL requires copyright to be assigned in the circumstances where there is copyright, but the public domain is not such a circumstance, so it's GPL-compatible. slopcode is not copyrightable, but editing it even a little places it in the purview of human creation, so this isn't really a problem in practice; whoever fucks with the slop well enough to get it to run would be the copyright holder. the question is: does fucking with slop create a whole new derivative work, entitling the unfucker to copyright over the whole project, or does slopfucking create a circumstance where only the human-effort modifications are subject to copyright within an otherwise public-domain project? I have no idea.