Ultimately it is selfish interest. Either because they literally have money invested or they are "losing" their childhood. But it's not disingenuous. It's how they actually feel. The area losing its "character" is an accurate description of that. It doesn't matter if I think or you think the mixed use zoning would vastly improve things long term. Doesn't matter how many studies are shown. Things will necessarily change in ways many people don't want and many times there are actual downsides for existing residents to make way for the new. Especially during transition periods.
None of these are arguments from me against new development or pushing past NIMBYs where they become intractable. But if development in Pasadena can maintain as much existing green space as possible and commit to building out more, it would be a lot palatable to the "natives". And I think it would lead to better results for future residents as well. I think it's okay that people want to live in a neighborhood full of quaint small family businesses and resist the Subway and the McDonald's and the Dollar General. But that's "NIMBY" too so where do you draw the line? We live in a capitalist society after all, and the only thing preventing these large mega-corporations from being absolutely everywhere are the few NIMBY willing to say no to it with the little power they have over their slice of the world.
Again,
I'm not saying the feelings are disingenuous or that you can't object on personal grounds.
I'm saying that using 'character' as a catchall for things you personally don't like is disingenuous. It's hard to argue against since it can't be defined.
Don't like multi-story infill? fine. Argue against that specifically and provide reasons that don't rely on something indefinable. Personal feelings about specific issues are a fine reason for arguing since those can be dealt with. I can argue that parking is or isn't an issue and can be mitigated. I can't really argue that the neighborhood isn't losing its character.
I can do the same thing by invoking "problematic" which carries social connotation in the same way that "character of a neighborhood" carries social meaning. If I say an argument is "problematic" you can't really rebut in any meaningful way because you don't even know what I mean. If I say an argument is using false premises or invalid logic, there is a discussion to be had.