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You can deorbit things by pushing them "up" from Earth which lowers their perigee on the other side of the orbit.

A ground based high energy laser could ablate material from Earth which would provide propellant mass and incrementally knock objects into deorbiting trajectories.

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And what happens to the ablated material? One large stage that is easily tracked via radar is preferable to tens or hundreds of milimetre size chunks that could potentially flake off while ablating the surface of a rocket stage or derelict satellite.

Ablation turns the material into individual molecules.

Yes, when done perfectly in a lab. Under less than ideal conditions, temperature gradients cause cracks and then flakes are released and expelled.

Drag brings those flakes to the ground.

Flakes of solid material are typically far more than dense than structures made of the same material. Therefore flakes' orbital lifetimes are likely longer than structures made of the same materials.

Pushing "up" on an orbiting body causes no change to the altitude at the other side of the orbit (that is, 180 degrees around the orbit). However, it does raise the orbital altitude 90 degrees ahead, and lowers it 270 degrees ahead.

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