Other than a mindless fearr of a hard fork, give me 1 solid reason based on logic against a block size increase.
1) Security risk of a DOS due to quadratic validation problem.
2) No hard fork experience.
3) High risk of damaging merchants and businesses that do not manage to update in time (if the activation parameters are improper such as with Bitcoin Classic).
4) Higher storage cost.
5) Higher bandwidth cost.
Even if we disregard the 4 latter, the primary issue is still the security risk.