I'm a bit surprised to see all the vehemence towards the Giants on AN. I need to write my thesis, so this'll be short.
I was 9 months old when the A's won in '89, and I've been an A's fan for as long as I can remember. Mostly, it was because I was (and continue) to be enamored with Rickey. I always identified as an A's fan first, but I've also always rooted for the Giants. Watching a VHS "Champions by the Bay" dozens upon dozens of time as a kid, I always thought a Giants-A's WS matchup as being pretty ideal. The convenient thing about living in the Bay is you have two teams to root for. I've always seen that as a good thing. I guess living in a bi-religious family I feel okay reconciling two faiths.
The other part of this is that I have family roots going back at least four generations in the Bay and specifically, San Francisco. My grandmother was a huge Giants fan, and she passed away shortly before they made the WS in '89. My mom and dad are Giants fans. Anyone who's had family in the Bay for more than two generations likely has some Giants fans in their family. I have, above everything else, pride and affiliation in the region I come from – the Bay – and I think anything that produces so much pleasure for so many people in my community is wonderful.
This is against George W. Bush's baseball club, mind you. I cannot ever possibly root for a club associated with that schmuck. (I'm sure some of their fans would like to see me deported too.) I root for region and culture and people who don't want to see me deported.
Pareto optimality. I don't think the Giants winning takes anything from the A's. We all know they will be rotten next year. They may draw more attendance next year away from the A's, but the A's attendance is piss-poor anyways, and that fact alone doesn't affect Wolff's bottom line with revenue sharing.
There was one period when I recall identifying as a Giants fan (in addition to being an A's fan). That was around '97, when the A's had Blake Stein and Jason McDonald and Mount Davis had been around for a while . We could only afford upperdeck seats at Candlestick. When the Giants moved to Pac Bell, I felt abandoned. They shifted classes and demographics, they became a new baseball club. The Giants are slightly less corporate now, so I feel a bit better about rooting for them.
Bottom line: baseball is cultural for me. When/if the A's move to San Jose, I'm not sure I can remain a fan. They'll be abandoning their blue-collar, scrappy, underdog fanbase. I'm an A's fan because of who and what they represent. Otherwise, it's like jingoism or nationalism. The flag's gotta mean something.