This part kicks a lot of sites out of workplaces via firewall. Simply put, all links out of a site are scanned and if they link to a site that has malware on it, bam, it goes on a block list. Every link someone adds to this site increases the chance of that. I'm thinking, for example, about all the Examiner.com blog links. That site is so full of malware and tracking software it isn't even funny.
That's the most logical explanation. There's nothing on FR itself that could be considered malware or "dangerous". If someone on FR posts a link to another site that is considered questionable, FR might get blocked.
I don't yet see any evidence of a grand conspiracy here, although I'm willing to be corrected.
Every time I go to the IRS page to get some forms, my firewall and anti-malware software goes nuts. Almost shut down my old computer it was so persistent.