I'd say that for a couple of generations at least (and perhaps further) those taking part in Guy Fawkes bonfires and fireworks did so because it's the thing you do on that day, not out of some anti-catholic sentiment. So while it's likely a big part of how this "celebration" got started, and everyone will have learned about it all in school, I think the vast majority of people in Britain itself (i.e. Scotland, England and Wales) don't believe or realise they're taking part in something with sectarian roots. I can't speak for how people in Northern Ireland feel, however.

I was never interested in it, really, as I don't like fireworks. I did find it entertaining once when I was a kid, we had just moved to a fishing village and they were struggling to light the bonfire. So some guys poured petrol on the fire, lit a flare and threw it on the bonfire :D