No one except you is making any such claim.
You will have to be more clear. You do not indicate which claim you are referring to.
Are you referring to the claim that the North invaded to abolish slavery, (made by most who defend what they did) or are you referring to the claim that they invaded to stop independence for the Southern states, and later added the goal of abolishing slavery after it looked like they were going to win?
From the evidence I can see, the Northern motive for entering the war were to force the South back under the control of Washington DC. That was the one non-negotiable point that was consistent throughout the war.
It was made very clear by the Union Leadership that the South could keep slavery, but they couldn't keep Independence.
My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that.
-Abraham Lincoln-August 22, 1862