I like dogs. Hitler liked dogs, too. Therefore I must be as reprehensible as Hitler.

That is an example of an ad hominem attack. Taking an aspect of a person’s personality and using that to denounce everything that person does/professes/thinks/believes. A particularly favourite accusation is, ‘Well, she’s a [Tory, Labour, Republican, Democrat] so you can’t believe anything she says.’ The ad hominem attack is the purview of those who have no legitimate argument against a person for whom they don’t care.

Anton LaVey is often the target of such attacks. No matter what his biography actually was, his philosophies and beliefs are still sound.

Ray Charles was a drug addict. Martin Luther King, Jr. was a womanizer. Gunter Grass was a Hitler Youth, etc, etc. Would you like to have your entire life judged by the least attractive aspect of your personality? Or would you like people to consider your entire contribution to the world?