[naikrovek]

the solar sail would need to be incredibly large for a craft that can move to arbitrary locations in orbit for the purposes of de-orbiting satellites, which means it must have large sails so that both the de-orbiter and the de-orbitee can both be moved via sunlight alone, and achieve the required thrust vector in a reasonable amount of time (this de-orbiter must de-orbit many satellites, remember?)

the larger the sail is, the more likely it is to be affected by space debris at any given moment.

debris passing through a taught mylar solar shield will tear holes in the mylar which are the shape of the debris passing through. any sharp corners in the debris will leave a sharp corner in the hole, and those corners are going to become tears the next time something passes through nearby. the tiny holes become large holes pretty quickly.

other materials will behave differently of course, but i don't know of any solar sails at all, never mind ones made out of not-mylar.