Should you feel bad for hitting the pedestrian? Yes. I bumped one and felt bad. It's just human. We don't like hurting other people so if we do, we feel bad. Was there much you could do? Filter on the right could've helped in this incident, but then someone walking the other way could step out and the result would be the same. Cycle slower? Again, it would've helped with this incident. but I'm not convinced it's the best solution long term.
If a ped steps out from the front of a wagon, surely they're obscured from view until the moment they actually step out? 20 mph, 10 mph or 100 mph (Rocket assisted, of course), they're still stepping out and leaving you no reaction time so what does cycling slower achieve? Yes, if you hit a pedestrian whilst you were travelling at 20, if you'd been cycling at 10 mph then they would've stepped out with enough time to react. By the same token, if you'd been cycling at 10 mph and someone steps out right in front of you, if you'd been doing 20 you wouldn't have been there when they stepped out
Without stopping and dismounting whenever traffic is stopped and sight-lines are iffy, I'm not sure what sorts it, being honest. Segregated cycle track? Helps with the lack of vision from stopped high-siders, but people can still do silly things and step into your path without looking. Ride around at walking pace? Again, people still can step literally into you, so even that doesn't guarantee anything. Public information campaign telling pedestrians to look both ways when crossing the road, not to cross around large vehicles, and to try and look where they're going? Probably a good idea, but people might be too engrossed in walking out from behind a bus whilst staring at their phone and listening to their iPod to notice the adverts so...