I think you mean't "To dispose of any presupposition as irrational, simply for the sake of logical consistency, is an responsible way to live." Not to, is irresponsible.
You can have a rational conversation about anything as long as you don't use irrational arguments.
Solipsism proposes that the world is just a creation of the mind.
However the only way to define the mind is in the context of the world outside of it.
So no, the world isn't just imagination, and the imagination isn't just an artefact of the world. You can only define each one of them in function of the other.
Just like you can't define good without bad.
No one I know has been able to define a rational purpose for their life. You can't have purpose to yourself, just to others. Either way it's an infinite purpose chain.
I can prove you have no purpose to yourself.
If you say you have purpose to yourself, you then ask: but then what's the purpose of myself? You enter infinite recursion.
You can only have purpose to others.
Life can only have purpose to something else other than life.
Does that other thing matter?
Have you ever considered why you value what you do? You can't have a rational conversation and say doing whatever you value is justified by the act of valuing it.