The Buddies boardroom boss joined with his counterpart from Ross County, Roy MacGregor, to sink the 12-12-18 plans on Monday over fears fans would not back it.
That lead to angry rebukes from Scottish Premier League chiefs such as Aberdeen chairman Stewart Milne and Hearts chief executive David Southern as they blamed the pair - and Gilmour in particular - for endangering the future of Scotland's clubs.
But Lennon stressed Gilmour has to make the tough choices that he believes will be best for Saints.
He said: "It's not been an easy week for us here but the chairman is the voice of the football club and the decision he took was not done lightly. We're all 100 per cent behind him.
"But I will ask you this question: Do you really think there is any other football club that doesn't act with a little bit of self-interest for their own club? You have got to look after your own house."