As a general rule, civil suits for copyright violation exist to recover damages caused by the violation, and prevent future damage thereof. Under that standard, a rather novel form of copyright seems impossible to defend: copyleft licenses.
Copyleft, the common descriptor for copyright licenses which allow free use provided any derivative works are released under similarly free terms, attempts to force the spread of open content (most typically software) through clever usage of conditional license grants, most notably used in the GNU General Public License. But how could this possibly be enforced in court? Because this sort of license was designed to guard against violation of one's beliefs, rather than financial damage, in the case of a violation, it would seem one could only claim moral damage.
In short, how would one possibly justify a copyleft violation suit in a court of law?
For the purpose of this question, I'm referring alternately to either US law or EU law, as I'm curious about both given the clear differences in intellectual property law between the two.