You can detect the effect of gravity... but you really cannot detect gravity. Place yourself in free fall and then try to detect it. It's there. But where? And in what direction is its force vector? How many gravity sources are there? Where? Can you detect them?
What do you mean by "detect"? How is your feeling of weight different from your feeling of hot or cold, or from hearing.
Bear in mind that our inner ears are rather sensitive to the direction of gravity (or acceleration, if you will).
But the argument isn't about semantics. It's about whether a phenomenon is regular and quantifiable and subject to study by science.
The claim was made that gravity is just as elusive as God. I'm rather amused that Newton's icon of scientific investigation is being attacked by creationists. It's a real hoot.