I don't listen to Lauryn Hill's music, nor am I Catholic, but I still think it's horrifically obnoxious to do what Lauryn Hill did - you don't accept an invitation to do a concert and then insult your hosts, whether you have a good point or not. Have a press conference announcing you're declining the invitation and state the reason why. Convince the other artists not to attend. There's so many other ways to protest. This is not exactly "constructive engagement".

US singer blasts Catholic Church at Vatican Christmas concert