Three days before the Mandalay Bay shooting, I stayed 3 nights at that hotel for a BICSI convention. Thirteenth floor.
Although there was valet parking, for a smaller fee I chose to self-park in the multi story parking structure. To discontinue self-parking and only offer valet-only service in order to scan people/luggage would really slow down access in the most inconvenient way.
Mandalay Bay has CCTV cameras throughout the parking structure. A camera was discovered in each of the 24 hotel elevators. I lost count how many cameras I noticed in the lobby, corridors, casino area, restaurants, and food court. Lots of coverage. Probably only the casino cameras are monitored live, just my guess.
I left my luggage in the car and stood 30 minutes in the check-in line at the hotel lobby. Large open space check-in lobby at Mandalay with doors and floor-to-ceiling windows everywhere. Bullet proof glass? Doubt it, but these hotel casinos make pretty good money and can afford to have it installed if they so choose. Exits were clearly marked to my right and behind me, and an 'employee-only' corridor was in front of me. It's habit to look for these things everywhere I go...just in case I need a fast exit.
From the street level, there are so many doors leading into this hotel/casino it would be an arduous task to post security inspection points at each door. Casino/hotels make money by people coming in off the street to gamble, or eat at one of their many restaurants and clubs. Some have movie and live show theaters inside, etc. Restricting the easy flow into a casino/hotel would negatively affect business (loss of money).
So how does one secure such a structure? I don't have that answer. It will take a balanced approach. Do we in the United States adopt the stricter European 'airport security'-type model by valet parking, body scans, x-ray machines, etc? Do we make 'laws' requiring hotels/casinos and certain other types of businesses to provide security guards and scanners at all entrances (at their own expense)?
In addition to businesses providing security for their customers, maybe we should put the responsibility for our own safety squarely on our own shoulders. Maybe we should be teaching people how to be more aware of their surroundings, how to detect possible bad situations, how to deter and/or avoid them, and if the worst happens, how to defend themselves.
As another person in this thread expressed, my heartfelt prayers go out for those who lost friends and loved ones in this horrible tragedy.