It's been a few years since I've seen anything relating to the Stargate, but what I recall from the show is that the episodes go something like this:
- Stargate team jumps through the gate to another world
- The inhabitants of that world have a problem
All well and good...but that gets me thinking, why doesn't anyone ever come through Earth's Stargate?
The Goa'uld could certainly benefit from a surprise attack in the middle of their base, especially since they have superior technology to Earthlings, and spaceships that could traverse the distance to invade should they render the Stargate inoperable - they have nothing to lose from an attempt.
But even if we don't include the Goa'uld, why don't other species ever cross through the gate in the same way humans constantly hop through to visit other worlds?