Political activist Jolovan Wham said that from the start, it was "pretty clear" to him that the Singapore Government and political establishment would not be happy with the meeting he had with Malaysian Prime Minister Mahathir Mohamad recently.
"But what I do on my seditious vacation is really none of their business," he added in a Facebook post yesterday.
Mr Wham, with historian Thum Ping Tjin, journalist Kirsten Han and graphic novelist Sonny Liew, had met Tun Dr Mahathir last Thursday in Putrajaya.
They were joined by political exile Tan Wah Piow and Malaysian social activist Hishamuddin Rais.
Last Saturday, Marine Parade GRC MP Seah Kian Peng wrote in a Facebook post that Dr Thum had invited Dr Mahathir to "bring democracy to Singapore", and that "it appears quite clear to me that PJ Thum does not wish Singapore well".
Ms Han responded to say Mr Seah's statements were "baseless", and called on him to retract them.
On Sunday, Home Affairs and Law Minister K. Shanmugam told reporters it is an absolute no-no to invite a foreign politician to intervene in Singapore's domestic politics.
Mr Wham, responding to the criticisms, said in his Facebook post that "lobbying an over-seas politician on political and civil rights in your country is nothing new".
"Activists all over the world do it. The most recent example that comes to mind is Hong Kong Occupy activists lobbying politicians in the United Kingdom and United States. International political pressure is part of activism," he said, referring to the territory's Occupy Central pro-democracy movement in 2014.
"Even if PJ had asked Mahathir to 'bring democracy to Singapore'... what is wrong with that?"
One may question Dr Thum's choice of person to lobby, but that is a purely strategic question and has nothing to do with "foreign interference" or subversion, Mr Wham said.
"Real interference is when a foreign government tries to rig election results or breaks into your systems and tries to manipulate information and data."
Mr Wham ended his post by saying: "If there is anyone who is being divisive, it is Shanmugam and Seah for their irresponsible comments, and for unleashing a mob on PJ Thum and Kirsten Han."
Ms Han has said that she and Dr Thum have received death threats and accusations of treason since Mr Seah's Facebook post last Saturday.
Mr Seah, in a new post on Monday, called on netizens to maintain a certain decorum in their comments and "not get personal or abusive".