Since the original email was apparently sent to all in the building, I'd reply to all asking if Building Maintenance / Facilities is accepting liability for any loss or damage to bicycles locked to the bike rack that is lightweight and not secured. Sounds like they're too (expletive deleted) to confront you directly, so they're trying to shame you by broadcasting and getting all your coworkers to rag at you. Reply to all would be equally acceptable to share your concerns that they haven't addressed. Next salvo, should it come to that, would include the British Medical Journal's article that concluded there's a 20:1 benefit in longevity over death during cycling, and asking if it's company policy to drive up health insurance costs for everyone by discouraging someone who's trying to reduce medical expenses.

(If you couldn't guess, I don't like to play fair with poultry-excrementing bullies.)