You are comparing apples and oranges. One sided contracts are perfectly fine and morally defensible. Just don't sign it if you think it is one sided. However - duress is something completely different: a contract signed at gunpoint is of course not valid.
Banning "one sided contracts" violates the basic human right of freedom of contract.
But neither one sided nor duress are relevant here. Don't go to the concert if you don't think it is worth the cost of the ticket, Going to concerts aren't a human right, nor is forcing the seller of tickets to sell them at a, for you, acceptable pricepoint a human right. And it doesn't matter if the seller is a first party or third party ticket seller. Stupid socialist.