Think you got that backwards, considering those with cars are the ones paying extra fees (+tickets), thus subsidizing the rest of the students for whatever the college spends the funds on.
Second statement needs a source, and regardless it isn't a valid reason. Colleges don't decide how adults live their lives.
Parking spaces are not free. In city's they generally cost 3+ $ a day in upkeep and opportunity costs.
Also, collages accept students younger than 18 which are not adults and legally can't be treated as adults.
I'm very interested in the upkeep cost - do you have a source for that?
"A 1996 survey found that commercial parking operating expenses average about $500" per year. Construction costs Dallas $13,281 to New York $20,326 av $15,552. http://www.vtpi.org/tca/tca0504.pdf
However, opportunity costs bump that as for example it lowers the density of the area.
Also, some schools try to discourage car ownership due to the number of student deaths associated with drunk driving to and from parties.