In fact ignorance of law leads to more lawsuits than knowledge of it.

[Potius ignoratio iuris litigiosa est quam scientia.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

De Legibus [On the Laws], Book 1, ch. 5 (1.6) / sec. 18 [Marcus] (c. 51 BC) [tr. Zetzel (1999)]
    (Source)

(Source (Latin)). Alternate translations:

It is not so much the science of law that produces litigation, as the ignorance of it.
[tr. Barham (1842), Barham/Yonge (1878)]

The litigious spirit is more often found with ignorance than with knowledge of law.
[ed. Harbottle (1906)]

For it is rather ignorance of the law than knowledge of it that leads to litigation.
[tr. Keyes (1928)]

Ignorance rather than knowledge of the law leads to litigation.
[tr. Rudd (1998)]