Generally, not very effective (reentry vehicles are a quasi-execption), and they can be intentionally designed to be ineffective as weapons without seriously compromising their effectiveness at space travel. However, this isn’t so much about mass per se, but about sectional density and structural integrity, see me and CellBioGuy’s upstream comments for details.
How effective is a spaceship as a kinetic weapon, anyway? They’re not very massive.
Generally, not very effective (reentry vehicles are a quasi-execption), and they can be intentionally designed to be ineffective as weapons without seriously compromising their effectiveness at space travel. However, this isn’t so much about mass per se, but about sectional density and structural integrity, see me and CellBioGuy’s upstream comments for details.