I agree with your broad point, however giving locally can still be an effective means to distribute resources at a non-local level. A local community project that I’ve recently become a part of has links to other groups that operate on a national and international level. It’s hard to know what groups are trustworthy across a wide range of issues and scales, but it’s easier if there are some groups or campaigns that you trust.

As an example, I was recently talking to someone from a group fundraising for humanitarian aid in Sudan. I don’t remember the particular charity they were affiliated with, but I met them through a national event that involves a collaboration of many different progressive political groups and causes. At this event, there was also a lot of local level stuff going on (and I was there because I had learned of it through my aforementioned local group).

It’s not perfect, but it seems better than the decision paralysis caused by feeling insufficiently well-informed to know which fundraising efforts are worthwhile.