What do you do when someone comes to you with an idea you find hopeless or inadequate?

You denigrate the idea, saying it is a bad one and it does not deserve any of your time.

You force change onto the idea to make it fit with what you think might be a better idea.

You begin a conversation and try to compromise to get the idea nearer to you.

You support the idea and say you will do your best to help.

I guess much depends on how invested you are in the topic. A manager might find it difficult to support something that might take time and resources and return no results; a friend might be more open to keep their opinions to themselves and help instead.

Relationships are built and broken on these type of choices. Get to them with intention and care.