Football clubs are social institutions, in my view.
Despite what some people, and those temporarily in charge of clubs at various times, would sometimes like to claim, they were established to represent the geographical locality.
Some people argue that they were this in the past but are no longer.
But consider this. What difference is there between any football club - City, Unuted, Rochdale, Real Madrid, Santos - if their geographical location is stripped from them? Nothing. They would be a touring, faceless, cynical franchise without a home and without any culture.
Everything that any fan recognises as 'special' about 'their' club is determined by the location that they represent. The history of the club, the nature of the club, the culture of the support, the long term style of the football. Is their a difference between City and West Ham? Yes, and that difference is nothing about temporary success (or lack of success) or temporary players or staff. It is that one is an East End club, representing that area with that culture defining them and the other does the same in Manchester. Every defining characteristic about the clubs stems from the area they represent. Otherwise, there would be no difference between the clubs and they, and every club, would be soulless shells with very little appeal to anyone other than the most cynical.
So, if you 'choose' to shun a club that represents an area that you feel close to or connected to in some way, whether that is being born there, growing up there or being connected to it by family roots or some other connection, it does a disservice to your roots, in my opinion. Despite what we all think at times, football is not important enough to sell your soul down the river in pursuit of something more glamorous. Particularly as that glamour is, in the ranking of what is really important in life, will not actually have much impact on your real happiness (family, opportunities, sense of self worth, etc).
I absolutely understand people having nothing to do with a location but supporting them because dad (or someone else extremely close) did. It's a form of connection. Although they must be able to see that they would 'feel' it even more if City (or whoever) were still the same club but magically transported to represent the history and success of the town/city that they feel closest too.
But I can't really understand those who, as adults, claim 'passion' for a chosen club that they literally had nothing to do with at the time. Yes, I can admire the time and money spent to travel but, as an adult, who presumably likes to be able to understand what motivates myself, would always have a question about what motivates me to claim that they represent me. I get that some people will 'choose' an unrelated team as a child and children, as we all know, make immature and easily influenced decisions based on glmaour. I do wonder why those people don't question why they continue that mindset/choice into adulthood though.
Saying all of the above though, as stated, football isn't actually that important in life so whilst it's not important enough to shun teams that genuinely represent you and your roots, in my opinion, those choices also not important enough to be bothered about compared to really important issues in life.