Why it is that rare steaks are not a concern, but rare ground beef is:
The surface of any meat, be it pork, poultry, or beef can have contaminants from normal processing procedures. Beef is normally washed with a disinfecting agent before it is cut from the carcass. but that doesn't always remove all contaminants. With beef, the nasty little critters are only on the meat surface. When you cook a steak, or roast, the surface is heated sufficiently to kill and pathogens. The inside of the meat is still pristine, and so is safe to eat.
With ground beef, those pathogens are mixed throughout the meat, and if let sit on a shelf for a few days, multiply all through the meat. Generally, if the meat is ground the same day, and comes from a reputable butcher, and kept below 40' F., it can be eaten rare, or medium rare with no problems.
Steak tartar is made from beef that is ground just before serving. It is especially popular in Europe.
I have eaten raw beef with no ill effects many times. I've even eaten raw ground beef when I knew it was ground just before I purchased it.
I have never had food poisoning, and I'm hitting 58 years of age in a about a week.
Also, in years past, most beef came from local sources, and you knew your butcher. The butchers took great pride in their work, and took great pains not to sever the intestinal tract of the animals. The meat was clean from standing on the hoof, to the shelf in the meat market, unless you lived in urban areas, where meat often came from large slaughterhouses. Chicago was infamous for poor meat handling procedures, hence the famous book that single-handedly brought such practices to the public eye. Chicago meat packers were forced to clean up their industry by law.
The best burger I ever ate was in Olimpia Washington, and was served medium rare. It tasted like a really great steak. I was hugely impressed. I still haven't been able to re-create it.
But that's ok, 'cause I make a pretty good steak.
With both pork and chicken, nasty microbes and parasites live in the muscle tissue. This why they have to be cooked to sufficient internal temperatures to kill the critters.
Seeeeeya; Chief Longwind of the North