Trunk or Treats are awesome. I don't know about the net thing the OP is talking about, but we had a lot of them in Colorado. At a church or a school, usually a different night than actual Halloween, they'd have hot chocolate inside (usually pretty cold there at the end of October). Some had various carnival games and stuff, lots of fun. Cars were decked out with decorations, it was pretty fun.
It creates a pretty fun environment for the kids, and we'd still go house to house on actual Halloween.
ETA- looks like the one the OP is talking about is happening on 10/30 in the morning, so it doesn't replace trick or treating, just an additional party for the kids. Not sure what the gripe is about.