Why did Wilson argue for neutrality in World War 1?

Simple. The German U-boats sank the Lusitania which killed many American citizens on board. Public outcry was too abundant for Wilson not to act.

Though the Lusitania was disguised as a passenger ship, it was secretly carrying munitions to Britain, which is why it sank so quickly when the torpedo hit it. It caused a chain reaction.

So, regardless, the U.S. had too many interests involved and would have joined the war eventually no matter what.