Why do rabbis allow hechsherim on junk food and other foods which are clearly bad for you health? Many products are clearly not good for you such as soda pop, baked goods with trans fats, food with preservatives, processed meats, etc. yet they are certified kosher.
My Rebbe Rav Shmuel Dishon (mashgiach ruchni Karlin Stolin) once asked us how do we think Kashrus organizations are allowed to issue "kosher" status on things that are damaging to the human body (unhealthy foods etc.) ?
We didn't know. So he answered, that all foods can be good in measure. Sugar can be good sprinkled here and there. Even a fattening sugary cheesecake can be a kosher treat at the right time and place. However, overindulgence is a choice. It is overindulgence that makes some foods dangerous. That's the consumer's business, not the Kashrus industry's business to regulate. The individual hechsher is only able to determine if the ingredients fit the rules of Kosher foods permitted by the Torah for a Jew to eat.
kosher certification can be given for anything that includes only kosher ingredients.
So an item that includes anything like not kosher animals, milk and meat together, or anything else that's not kosher, those products will not receive a hechsher.
But, any product that has all kosher ingredients, why should it not be kosher (as long as you don't mix milk and meat..)? Kashrus does not depend on health. There are many healthy foods that are not kosher, and so too there are many non healthy foods that are kosher.