It's a statement I've heard several times in the last few months. I'm not sure why - maybe it's one of the urban myths making their way around the internet.
The statement is: the shape of humans' teeth is proof that humans aren't meant to eat meat. (Meat-eating animals have canine teeth meant for tearing up meat - humans don't have those, so conclusion being, humans shouldn't eat meat.)
This statement makes about as much sense as saying that humans shouldn't live in Finland because they don't have fur to protect them from the cold.
Well... humans didn't need fur to be able to live in Finland. They learned to make clothes and footwear instead.
The same with teeth: the shape of humans' teeth simply means that humans didn't use teeth to kill animals, or to rip up raw meat. They didn't need to. They used tools instead: arrows and stones and sticks for killing, and blades and fire for cooking/prepping. The shape of teeth is consistent with humans being omnivores - eating pretty much anything they can digest.
There is a bird living in Galapagos, a woodpecker finch, who uses pieces of stick to get insects out of holes it otherwise wouldn't be able to get with its much shorter beak. According to the tooth/meat argument, that finch shouldn't eat those insects either - it doesn't have a beak long and thin enough. But, the bird still eats them, because the finch uses tools which make up for the lack of physical features of its body.
Why would humans develop canine teeth if they didn't hunt prey with their teeth, like lions, and then rip up raw meat?
Besides, opposable thumbs are much more useful than canine teeth anyway...