Being backed into Japan Rail Sardine Express is hardly my idea of quick or convenient.
Aslong as you dont make a mess, i dont mind eating in public, opposition to it in my opinion is just another example of social taboo's against a normal thing,our ancestors ate meat from the newly killed bone, infront of everyone, without manners, humans need to eat, humans like to eat, aslong as its not inappropriate like im in the middle of actually doing something, I'll eat in public with or without peoples approval.
I dont do it because i enjoy being rude, i just dont respect silly rules like that, unless people are genuinly offended by the act of humans consuming food stuffs for energy, something everyone does everyday including the witness.
Now if i was eating amongst a group of starving folk, it would be rude not to share, but in japan on a commuter train, with resutraunts and food everywhere in that country, if you havnt eaten before, or not gonig to eat at your destination, then thats your fault to be honest.