Have you ever stood in a line diligently, without breaking it etc and have seen ppl break the queue, cut lines and throw attitude? Ok.
Have you ever stood quietly in traffic and have seen unruly cars break line and try to enter from right and have caused bigger jams?
Have you paid your taxes on time and correct amounts but see that irritating friend who cheats?
Now Imagine a businessman who pays VAT/Excise diligently but another one cheats on it and offers goods at lower price and all customers go to him? How would u feel?
This is what is VAT v/s GST. GST doesn't allow dishonesty. As simple as that.
Guess who is whining? :)