So far  i knw i don't think e-ticketing has much more disadvantages than it innumerable advantages. 
however , it has some disadvantages like :-
1. many people r unaware about it those who live in rural areas . so awareness has to be spread
2.a computer crash could cause a passenger's reservation and other information to simply vanish

i think people who are poor in technological problem will face this problem

hope it helps

1 5 1
1. people who use the electronic system become lethargic and exhibit their laziness
2. if u are travelling with a ticket in your hand u exhibit ur responsibility