How Do We Know Laws of Logic Are True?

A few days ago, I made the following post on Facebook:

If logical truths are knowable, then Christian theism is

true.

Logical truths are knowable.

Therefore, Christian theism is true

One comment on that post went like this: 

“An intelligent unbeliever would have a bit of a field day with this.  

Why does your conclusion, above, necessarily follow from the premise?  

We could just start making up any "if, then" statements here, but that doesn't make it ok.  

I'm kind of confused on this one.”

I gave a brie...