I've heard that version before, but the Ethiopian idea always seemed much stronger to me. That Bono was inspired after visiting Ethiopia with Ali, when there was the great famine (I think it was 85, sorry if that's wrong). The idea of the streets with no name came from the endless rows and rows of makeshift tents that were put to up to shelter all the starving people.
A lot of the lyrics fit in with this idea too. The lyrics in the first verse seem to suggest that he is frustrated and sick of all the dying and that there is so little that can be done. He wants to "run and hide" from it all. These thoughts are possibly mirrored in those of the famine victims themselves. The idea of "tearing down the walls that hold me inside" seems to suggest he desperately wants to do all the things he can't do to try and save these people.
In the second verse the real thing that stands out for me is "I wanna take shelter from the poison rain". To me this suggests the metaphor that the poison rain is the lack of rain which is killing thousands of people, as poison would.
In the chorus we have "And when I go there, I go there with you. It's all I can do." This seems to show the idea that Bono went there with Ali and that it was quite literally all they could do - despite wanting to do more, they couldn't. Given that it seems it was initially Ali's idea to go, the words make sense.
In the third verse, "the city's a flood" gives me the impression of a flood of humans, making the makeshift city swell. "And our love turns to rust" is perhaps that despite all their hard work and caring, people are still dying and "turning to rust". The idea of death seems to be picked up a lot with the persistent use of the word 'dust' in the song. Finally, "High on a desert plain" could well be Ethiopia given that the country is a desert and is quite high above sea level.
As I say, this is just my interpretation of the song from things I've read and how I see the lyrics. U2's songs are very often ambiguous and about more than one sole thing, so it is entirely possible the Belfast idea fits in too, but for me the Ethiopian theme sits better.