The immunity granted to MPs speaking in parliament allows them to speak without fear of reprisal and harassment, and when fairly applied, is a good one. And it is up to an MP's peers to correct and where needed punish him. But as indicated in my example, Singaporean's refusal to elect a meaningful opposition has allowed the PAPzis to abuse this process, as they have with so many other aspects of politics in Singapore.
And they will continue to do this as long as they have more than 2/3 of the seats in parliament.