I have seen this stance taken by QXP that taking a second wife may be wrong.
4:3 If you fear that you (the society) shall not be able to do justice with the orphans, (as may happen in times of war and political turbulence, the government shall announce a state of Emergency), then, in order to accommodate widows and orphans, men of sound finances and character shall be encouraged to marry these widows; two, three, and four (4:127). But, if you fear that you shall not be able to deal justly, then, you must not take additional wives, and may continue with what you already have (4:129). This will be more suitable to prevent you from doing injustice and face financial hardship. [Second marriage during peace time is a frank violation of the Qur’an – note ‘If you fear’ in the beginning]
You: I would argue every man who takes a second wife is not a Muslim....
Me: On what grounds would you call him a non-Muslim? He may be a wrongdoer or violator of a law.