Well, that is the government's argument and let's see.
The Home Affairs Ministry's Excuses
According to the PAP, an Australian clergyman was turfed out of Singapore for interfering in domestic politics. This Anglican priest from Christ Church St Kilda in Melbourne, James Minchin, has irritated the pensive PAP way before in his book on former PM Lee Kuan Yew, No Man is an Island, where he resented the myth of the philosopher-king who led Singapore from 1965 until 1990.
In the SDP video Let's Talk, SDP interviewed Father James Minchin and he also makes no pretense that he is a political and social activist. Stressing his moral authority as a priest, James Minchin also made it a point to wear his white priest collar and black shirt. So there is no smoke without fire in the PAP being irritated with him subtly using religion to assert, and his affinity with SDP.
The Ministry of Home Affairs elaborated in its statement on barring the priest from entering Singapore that Father James Minchin came last year and shared openly his view that the law was corrupted and the clergy's integrity and independence questionable.
Hypocrisy, SDP-PAP and Politics as Usual
Was Father James Minchin interfering in Singapore's politics as the government claimed he was? He certainly is no apologist for the PAP government and the injustices he saw e.g. he said in the SDP Let's Talk about the government selling power generation to foreign investors, "for the government to allow foreign forces whether from the east or west, market forces to come in and control key sectors of the economy, key sectors of the social fabric, seems to me to be quite counter to the whole sovereignty of Singapore shaping its own future."
There is double hypocrisy here by both the PAP and Father James Minchin. The PAP allowed foreign investors into the economy but not foreign observers into Singapore saying what they think about Lee Kuan Yew's politics. On the other hand, Father James Minchin complained about foreign investors undermining the economic sovereignty of Singapore but not foreign observers like himself talking about social injustice in Singapore and undermining its political sovereignty.
However, the simplest reason obvious to all on why Father James Minchin was abruptly made to fly back to Australia was not because he was complaining about the PAP as there are hordes of foreigners who do that e.g. the foreign talent academics in the local universities. The reason was because he was allied with the SDP while he was complaining about the PAP. If it were not for his SDP links as can be seen by the backing loud calls of injustice by SDP members criticising Father James Minchin's persona non grata status, the Anglican priest would have been unmolested and left alone.