On the assumption that alcoholic drinks are 'hard' drinks. So non-alcoholic drinks are soft drinks.
Yes. Religiously observant Jews will only drink kosher soft drinks. Most major brands are kosher.
Because it is addictive.
you don't
Diarrhea makes you dehydrated very quickly. Soft drinks contain very high amounts of sugar, which also dehydrates you. So drinking them when you have diarrhea will only make you dehydrate even...