Why do people share? It's contagious, six-year study of Hadza people shows. In the modern world, people cooperate with other people including strangers all the time. We give blood, tip providers of various services, and donate to charity even though there is seemingly nothing in it for us. Now, researchers who've studied Hadza hunter-gatherer people in Tanzania over a six-year period have new and surprising insight into why people work together. Source 5a.
It really just depends on the situation. If it's for a survival setting of life or death, sure. But if it involves something more generic like a party group sharing one snack, I detest the idea to even go close due to poor hygiene.