The reason we are against it is because DarkRP is explicitly design in such a way that if ever you did need to edit a core file, you could do it without needing to touch the core files. This is because for every update from Falco, downloaded to a local copy of DarkRP, the chance of the file that includes your modifications being changed increases. This would mean that your work is overwritten. That’s not so bad if your modifications span only 1 file, but if they span numerous files, then an update would break your installation because your additional code is now not functional.
This again isn’t too much of a problem, but given that most times that a DarkRP error crops up, the first thing people do is post here, it then becomes our problem. The first thing we would normally do is ask for the trace of the error so we can determine where the error lies. If the error comes from a core file, then it means we can’t apply any of our normal logic, because we then have no way of knowing what i causing the error.
TLDR: Don’t edit the core files, basically.