Okay, final update with working solution:
Just hours after figuring out the lines of code to remove (which literally took all night whoops) my host got back to me saying their antimalware was responsible for the problem and they'd fixed it.
So, for other people experiencing this problem:
Step 1) Contact your host explaining the issue and they will hopefully add the exception. My host is not a small host, so I suspect a few people might suddenly have the ability to create working installs now.
Step 2) If your host is crap or there isn't an antimalware problem, extract the Campaigns.php file from the installer ZIP, remove the four lines outlined in my previous post, and hopefully that will help!