I like zebra crossings, it takes a little of the power away from motorists back to pedestrians.
If I'm on my bike I stop at zebra crossings unless it's really late that I spot anyone. But many motorists don't even look to see if there is anyone waiting.
As a pedestrian I march straight up to them and step out, if you don't the traffic won't stop. I'm fit enough and so far good enough at judging the traffic to make it work, and I'm doing it for those who are a lot more wary. Occasionally a car has to stop when it thought it wasn't going to, and I've had ones that have continued through even if I am on it. But I think you should stop if you see someone waiting, rather than having to see them step onto the crossing. I spent too long as a parent with young children who couldn't take those sort of risks.
That said sometimes especially if it is a bike approaching I've been know to delay approaching it so they can cross, or to wave them on if I'm the only pedestrian crossing.