What is a word that describes an opinion that nominally supports one opinion but in practice hurts or discredit it?

Other than the word that describes the opinion, is there also an adjective that is used to describe someone who thinks or pretends that they are on your side but their action is hurting you or your interest.

Sample Sentence: Edward is pro-gun but he lives in Chicago where gun control is very popular and he might face consequences such as being alienated around his friends if he decides to directly advocate for pro-gun policy. So he tries to indirectly advocate for pro-gun policy by giving an [word] argument which is an extremely flawed anti-gun argument that indirectly points out all the con of gun control while failed to mention all the pros.

Backstabber doesn't feel like the right word.

Solution 1:

This is called Straw man

an argument, claim, or opponent that is invented in order to win or create an argument:

The idea that national identity will be lost as a result of European integration is just a straw man which he is wasting his time fighting.

[Cambridge]