If we do X, Y becomes more likely. Y is bad, making a bad thing more likely is bad, therefore doing X has a bad consequence. That isn't a fallacy at all, it's

If we do X, Y becomes more likely. Y is bad, making a bad thing more likely is bad, therefore doing X has a bad consequence. That isn't a fallacy at all, it's just an argument that requires you to establish its premises, like all sound arguments. People call it a fallacy as a pejorative when they want to dismiss the legitimate concern and shut down the debate even in the cases where the premise is correct.