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 Aberdeen chairman Stewart Milne and Hearts chief executive David Southern as they blamed the pair - and Gilmour in particular - for endangering clubs' future.
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."
Had the reconstruction bid been passed, the SPL and Scottish Football League would have merged to offer Scotland's 42 clubs a range of benefits including a fairer share of sponsor income.
But talks have been put on hold following the SPL's failure to reach the required 11-1 majority. Lennon, though, insists a change of mentality is the most pressing requirement.
He said: "Change has to be right for everyone but it has to be addressed - but then who can really say what is right and what is wrong with any confidence? What will work and what won't? There is no league structure in the world that is perfect. None.
"But what we always seem to do is miss the opportunity to talk our game up. If there one thing that has to change, it's that.
"It's a Scottish mentality, not just in sport. We have to get away from all this negativity. We've just witnessed two of the best Scottish Cup semi-finals for years. The last six national cup finals have been won by six different teams.
"It's been the most competitive SPL in terms of how close the teams have been from second bottom to second top in the league's history. We even had 9,000 fans turn up for a First Division match between Partick and Morton. So I believe we have got to focus on the positive things in Scottish football."