Should a capital ship enter an asteroid field?

If real asteroid fields are sparse, why not send the capital ship through instead of using fighters?

Because the field creates a predictable ambush environment where an enemy can weaponize the asteroids; expendable scouts are the safer first move.

A real asteroid field may be much less dense than its cinematic depiction. The objection is tactical rather than navigational: an attacker can prepare the environment and detonate an asteroid near the entering capital ship. Destroying or moving a rock may be easier than defeating the warship directly. Sending fighters first reduces the risk to the fleet's most expensive unit and tests the suspected ambush. This applies the naval principle of scouting dangerous terrain before committing the main body.