Why was the North willing to go to war over Slavery?

I'm going to have to provide a bad answer because the question is ill focused, lacks evidence of research, and OP persists in debating in the comments rather than revising the question to resolve the issues about which comments have requested clarification.

The question seems to be an attempt to identify the role of American chattel slavery as a cause of the civil war. It contains the assumption that the North was responsible for pushing the South to war.

1. There are very few things in history that have a simple cause and effect relationship. (or perhaps there are, but we don't study them because they are trivial.) Slavery was a cause of the war. Fundamental tensions originating before the Constitution was a second cause of the war. Cultural divergence was a cause of the war.

2. The North didn't start the war; the South did. The South started the war because they didn't believe that the country could encompass the visions of both the South and the North, and because they believed that a non-military strategy would result in unacceptable losses for the South. They believed that the North wanted to eradicate the Southern way of life. The symbol of this was slavery, but their concerns were broader - there were irreconcilable economic and cultural differences - the 3/5 clause in the constitution, the Jay treaty, etc. etc. etc. The North sought a future for the country that included both freedom from slavery and prosperity. The North had made that clear from the foundation of the Republic.

3. The Southern political position was idiotic. The South sought a future based on a fantasy recollection of medieval life. Their vision was utterly unconnected from reality, and their economic principles were less sophisticated than your average third grader. They wanted to get rich by selling commodities in an unchanging world. They rejected industry, credit, capitalism, and every vestige of modernism. They created a fantasy reality based on a bygone era where land was more important than capital. They held dances and wore fancy clothes and each generation was financially, intellectually and morally inferior to the last.

4. It is not possible to predict a person's view based solely on their economic class/interest By the middle of the 19th century there was a consensus that abolition and civil rights were the right choice even if that choice involved some economic hardship. Britain endured huge economic hardship to fight slavery on a global scale. The New York Abolition society had existed since the beginning of the Republic. For some people, civil rights were a religious imperative; for others an ethical or moral imperative that trumped their economic self-interest. The South rejected this consensus, slowly transforming from irrational to delusional to pathological zealotry. In the end they started what was the bloodiest war in human history to that point in order to silence the people who kept demonstrating that the Southern way of life was delusional, disconnected from reality, immoral, and economically stupid.

Was slavery a contributing factor to the civil war? Yes. But slavery was one element in a mix of tightly coupled factors that ultimately resulted in irreconcilable differences.

Unfortunately a full answer to the question would be more than book length - there have been multiple books on the causes of the civil war, more books on slavery, more books on the causes of war. Questions that require book length answers are out of scope for H:SE (See [help]). This is a bad answer because it includes no sources, no evidence of research, and has a few paragraphs of thought about a subject where an encyclopedia would be more appropriate.