Agnosticism is the belief that truth cannot be obtained. Agnostics I have debated have been huge fans of quoting Socrates saying "I know one thing, that I know nothing." Not only is this blatantly contradictory, but it also means that for an agnostic to defend any worldview, or to oppose another, is ultimately dishonest. An agnostic walks up to a Christian and says "your Bible is wrong". Well you claim to know nothing, therefore you can't know if the Bible is wrong. You're either claiming to have lied about knowing nothing, since you are now claiming to know that the Bible is wrong, or you don't know that the Bible is wrong, so it's dishonest to say you do.
Another agnostic walks up to a Christian and says "you can't know if the Bible is true or not." But if you claim to know nothing, you can't know what other people know. The Bible says that you shall know the truth and the truth will set you free. So when you claim no one can know if the Bible is true, you're claiming to know that the Bible is not true.
Agnosticism is contradictory in every single way. It can only be selectively applied. No agnostic will say "I know one thing, that I know nothing" when they walk into a restaurant, or a doctor's office, or hop on a plane. You know that good food is healthy and poison will kill you. You know good medicine will heal you, but botched surgery will not. You know that a good pilot will fly you where you need to go, but a drunk pilot will take you down with them. Knowledge is freely available to us because we were designed with permission, ability, and command to obtain it. Agnostics are deceiving themselves when they claim to know nothing.