From 1981 to 1984, he was a lone voice against a whole house of PAP MPs. Anything he said would be jeered. Whenever he stood up he would be heckled. They gave him no respect whatsoever. To a large extent they did the same to Chiam, but JBJ was treated worse because he was more vocal and also because he was the first to break their monopoly.
Without JBJ there would be no Workers' Party of today.
That said, today's Workers' Party is a pale shadow of what it was under JBJ. They have, in some ways, sold out - they are too timid and many of them are fence sitters, afraid to take strong stands on issues. I'm not talking about 'opposing', they are simply not even taking a principled stand on many issues that are wrong.