You've obviously never worked on train dispatch, AOG.
At peak times you need to get perhaps 100 people off a train (with all their luggage) and then 300 people (possibly including two wheelchair users, and everyone's luggage) onto it, all in under two minutes.
Your idea is totally impractical unless the railways went to the vast expense of introducing the same system as operates on London's jubilee line.. (The Jubilee Line system, at some stations, has trains arriving next to sets of doors from the platform, with those doors only opening when the train doors do).
The Guildford incident is, of course, unfortunate but dozens of people get pushed into the paths of moving cars and lorries (during brawls outside pubs, etc) every year. Are you suggesting that every pavement should have gates which only open when a vehicle pulls up alongside?