The article defines "ecumenical" as stepping outside one's comfort zone. That is a liberal definition. I believe that conservative Lutherans see ecumenical is getting people into the comfort zone of agreeing on scriptural teachings. Liberal Christians have no problem worshiping and praying with Muslims, Buddhists, Hindu, Jews, and Christians of all stripes and spots. Conservative Christians take to heart the Bible's call for "complete unity so that there are no divisions among us" (1 Corinthians)and to "mark and avoid those who teach contrary to the doctrine you have learned" (Romans).
The problem could be avoided if each church and religion had its own worship and prayer service at a time of crisis rather than having a big "ecumenical" service. I have a hunch that more people would participate in the local churches than in the ecumenical service.