It sounds like you might be taking the 'bumpy surface' space-time metaphor too literally - I think it's only meant as an easy way to visualise the idea of curva

It sounds like you might be taking the 'bumpy surface' space-time metaphor too literally - I think it's only meant as an easy way to visualise the idea of curvature in more than three dimensions using our three-dimensional brains, rather than suggesting that there is actually a force acting perpendicular to the 'surface' the pulls objects into gravity wells. Were that not the case, then, as you say, the external force required to make gravity work would be gravity itself, which is a bit like the homunculus theory of consciousness (http://en.wikipedia.org/wiki/Homunculus http://en.wikipedia.org/wiki/Homunculus).