And for the record, "Streets" opening in the JT tour was probably the dumbest idea ever. It's the sort of track that can re-energize the audience, so why waste that potential on the opener? (Although in all fairness, that album kind of lacks a single song that really works well as a set starter)
I think it worked well in context, though. At the time, of course, it didn't have the iconic live song status that it does now. That title belonged to Sunday Bloody Sunday and Bad. I'm sure they were just thinking of a new song with a nice build up and Streets fit the bill.
There's really only 2 kinds of openers for U2- come out swinging right out of the gate (Out of Control, Even Better Than The Real Thing, Zoo Station, MOFO) or have a song that changes tempo and builds to set the mood (COBL, Streets, Love and Peace, Breathe to an extent).
By 1987, they had plenty of songs to re energize the crowd throughout.
Fast forward to 2010 when they were considering opening Glastonbury with Streets (before Bono got hurt) and you're 100% right, that would've been stupid. It's considered THE live U2 song and is now an iconic mid to late set staple.
But 1987-1990, when it opened, it worked absolutely fine.
As for NLOTH:
I am surprised by the number of people who think Breathe was a great opener. I saw it and thought it did nothing in that role. I love the song, but not an opener. I even liked Stingray-BD better. For me, Even Better Than The Real Thing blew every opener since MOFO, or maybe even Zoo Station, out of the water.
Think:
Magnificent and MOS.
Magnificent rotating and MOS a likely staple for exactly the reason everyone mentioned- it seems so well loved by the band.
Want:
NLOTH, WAS, Crazy (album version).