I also don't believe that your favorite team has to be one that you've seen in person or the team that you first watched. It can be a team that you've never physically seen but you watch their matches on TV.
That's your fellow forums poster Ava Noble-Lazarus, summing up this exercise. You may read her post, and the other respondents, here and here, with a couple of stragglers from other fora I mercilessly spammed. Here are the conclusions I drew from the responses, although you may well disagree. After all, the responders were self-selected, posting on a soccer board means I probably got fewer casual fans, seventy or so responses doesn't even reflect the site, let alone the sport, and so forth.
That's part of the reason I'm not going to insult your intelligence by putting percentages on the responses. My methodology makes a Hillary Clinton push poll look like a CDC malaria eradication study, and if I were to try to make this look professional by saying "15% of fans support a team that they don't live near and adopted later in life," I would deserve to be struck by lightning.
Anyway, you all are people with stories, not numbers on a graph. Mm-wah!
That said, here's what I noticed.
You are much, much more likely to support a team that comes from where you grew up, no matter where you are now. I realize I didn't ask that many questions, but that's overwhelmingly the common factor in choosing a team.
AT THIS MOMENT IN TIME, you are actually less likely to support the team nearest you, the first team you saw on television, or even the first team you saw live. This makes no sense, and it's my fault for asking vague questions. There's a better-than-small chance that the first team you saw live doesn't exist anymore, if you're an American. There's an even better-than-middling chance the first game you saw on the television was the World Cup. You probably fell in love with the sport, and you may well have adopted a team from the tournament - but there's no reason it should have been from the very first match.
Do you follow a favorite player from club to club? Congratulations, you are a tiny, tiny minority of my respondents. Even in the unlikely event you picked a club because of a player, you're not disposed to support his new team. Further study is needed, depending on how liberally you define "need." But early returns show that if you wanted to gain lifelong fans by signing big stars, you are pursuing a path of rank folly. Looking at you, LA Galaxy.
If your loyalty changes, it's because you moved. But this is uncommon. So much so, that the next time you hear "You live here, you should support Fill In The Blank," you have my permission to shake your head condescendingly. Not saying it never happens. What's much more likely is that Where You Live Now Wanderers becomes a second-favorite, but your heart remains with Where You Grew Up United.
But the team you support may be brand-new, especially (obviously) those of who are American (or Tijuanense) (if that's the term)). Switching loyalties, once imprinted, is rare - but it's much more likely if a new team opens in a place you have a connection to. Almost by definition, this is NYCFC's fan base today, and the MLS fan base historically.
Question no longer, therefore, Major League Soccer's commitment to expansion. Opening a new team in a previously unserved market either creates new fans out of the ether, or at worst converts a fan of a distant team.
And if we project outward, those new teams will be the ones that our kids and younger siblings will have loyalty to, simply because of municipal or regional pride. Seattle and Portland claim multi-generational status, but NYCFC and Philadelphia can't. Those teams can claim NASL groundwork...but then again, Real Salt Lake had no NASL predecessor. (And it's very possible to overstate the importance of a mere NASL presence. Dallas and New York, fine, but Houston and Denver's 70's forerunners were nothing to speak of.)
So MLS (and NASL and USL) should add as many teams as they feasibly can, as fast as they feasibly can, BUT ONLY IF we're sure those teams are going to stick around for twenty years OR you don't mind the successor team thirty or so years later reaping the benefits.
Of course, I'm taking this incredibly unprofessional poll and treating it like it meant something, so, in the words of Alaska via New Mexico businessman Jesse Pinkman, there's that.
But the very randomness in what I saw, even though it's demolished a couple of my prejudices, confirms one I've always held. Clubs are like cats - they choose you.