Easy. The predominantly WP-supporting (note: not 'opposition-supporting') crowd here hate CSJ for 3 main reasons:
1. They blame him for ousting CST from SDP. Actually it was the work of the senior CEC members like Ling and Cheo - then-party-newbie CSJ was just a pawn in their hands ... but WP supporters are generally not known to be very sophisticated in sifting fact from fiction. CST was ousted, CSJ took over as Sec-Gen, therefore CSJ usurped the throne.
2. They are generally put off by CSJ's consistent stance on human rights and democracy and decry his early advocacy of non-violent civil disobedience to fight for basic freedoms of speech and association, and free and fair elections. No less a personage than Aung San Suu Kyi has said that democratic institutions are the fundamental guarantee of basic human rights. But folks here are brainwashed by the Pappies into thinking that confrontational politics is destructive, and that the best way of dethroning the fascists in power is to not rock the system and gain one opposition seat in parliament every decade by playing according to the PAP's rules.
3. CSJ has been persistently demonized by the MSM through the years, for obvious reasons. Intelligent people generally don't give much credence to the drivel churned out by state-sponsored whores, but there are many here who are taken in hook, line & sinker and believe that he really is the madman as portrayed by the media.
By the way, be careful: labelling LTK as pseudo-opposition could earn you a few infraction points from some of the mad dogs here.