This means using legislation to force your moral codes on someone else when they don't agree it is a moral issue.
There are many behaviors that virtually everyone agrees are immoral: killing, cheating, lying, rape, adultery, and so on. All of these harm another person.
There are other behaviors that affect only one person or a couple or a group of people who consent to the behavior: these include virtually all moral codes related to consentual sex between 2 or more adults of any gender. The only exception is adultery, because that is cheating.
Your holy book says that the second group is a sin and therefore immoral. Those of other religions and no religion disregard the authority of your holy book.
Therefore when you attempt to pass legislation regarding sex according to your holy book, you are forcing your moral codes on people who do not believe in them.
Of course that's what it is. You base your morality on an ancient book that not everyone recognizes the authority of. Some of it we agree with. The rest is unnecessarily restrictive for the sake of being restrictive.