A crowd estimated at more than 70,000 people on Saturday waved American flags, sang the national anthem, and called for the defeat of a Wisconsin plan to curb public sector unions that has galvanized opposition from the American labor movement, Reuters reports. In one of the biggest rallies at the state Capitol since the Vietnam War, union members and their supporters braved frigid temperatures and a light snowfall to show their displeasure. The mood was upbeat despite the setback their cause suffered earlier this week when the state Assembly approved the Republican-backed restrictions on union collective bargaining rights over fierce Democratic objections…