The law has long since been on the side of wrongdoers
Nonsense. If that were the case, we wouldn't have so many laws criminalising undesirable behaviour.
If you mean lawyers, in criminal cases they should operate under the cab rank rule and take on all comers provided that they are available. They don't know whether the accused is guilty and are perfectly entitled to test the case against their client.
So far as civil claims are concerned, there is rather more latitude and lawyers can certainly refuse to take on claims that aren't viable, and I think that is likely to be the difficulty with this one. When people are in public places like railway platforms they must be aware the CCTV is on and that they will be filmed, and indeed I suspect that implied consent to filming is written into railway bylaws. As I understand it, this railway company didn't release the broadcast, so the parent would have to find out who did - which may not be easy - and would have to consider whether that individual actually has the means to satisfy any judgment. The individual concerned has an argument that publication of the film isn't necessarily a breach of any privacy rights - after all, there are videos all over YouTube and the TV of people wandering around the streets. There is also an argument that, if there is any claim, damages should be limited to what would be payable for having your image released - which would be minimal - on the basis that any vilification that this young man has attracted is caused solely by his own behaviour.
One limitation on the suggestion that lawyers will take on any interesting claim is that of funding. This is certainly not one that is likely to attract a now-win no-fee arrangement, because the lawyer needs to be able to discern at least a reasonable prospect of winning. Legal Aid isn't available, and I can't seriously see something like crowdfunding getting off the ground.