Picketing itself isn’t “shouting down.”
In its simplest form it’s carrying signage. One can even be vocal without shouting anyone down, been there done that, there’s always gaps between speakers where picketers can add opposing remarks.
Don’t confuse leftist rioting, screaming, interrupting and wailing with conservative picketing, they just aren’t the same. The objective of the leftist is to drown out debate while the objective of a conservative is to encourage debate where there isn’t any.
Picketing necessarily involves interfering with someone else’s freedom to come and go as they please. People attending a concert aren’t violating any laws, or committing any moral infractions, why not let them alone and go after the source of your problems? Yell at Waters, not the people who just want to enjoy a show.