Well in the US and notably on AA I have found that those who wear Union lanyards are those who care the less, have the most attitude and are the most vocal. So yes any union apparel that I see worn by crews these days makes be cautious of what service I will get from those crew members.
Employment law is very different in the UK and US, so its not fare to compare an aggressively pro-employer regime (US) with a more employee-biased regime (UK).
The reason unions in the US are more aggressive and vocal is because the US is 30 years behind the EU in recognising that employees deserve some fundamental basic rights to be enshrined in law.
I'm not saying the EU model is perfect, personally I think it's got a tendency to go increasingly too far in favour in employees these days and should return to a more fair and balanced model.