At the end of the day there is no really "right" voting or "wrong" voting. Else there wouldn't be choices. So what if you're voting against your party? If Goh Chok Tong lives in AMK and hates Lee Hsien Loong, he's free to vote for the rookie WPers. Spoiling the vote wouldn't bring Lee down by one vote.
This is politics - including internal politics.
I'm surprised TFBH ranks this 100 times worse than not caring/looking after a ward. In voting, you have at least 3 choices - party A, party B or spoil vote. In serving a ward, there is no choice. You can say there is 2 choices - caring for the ward or not caring for the ward. But who stands for election not planning to care for the ward?!?!?! So option 2 is NOT a choice.
(However I think GMS comments have been taken out of context, I think he means lower priority rather than "not")