The Buddies and Ross County voted against the proposals at Monday's Scottish Premier League meeting, which would have seen the current four divisions reduced to three divisions of 12, 12 and 18 teams.
A majority of 11-1 of SPL clubs was required for the plans to be put before the Scottish Football League but the two clubs remained unconvinced and the plan was scuppered.
Aberdeen chairman Stewart Milne was furious with Gilmour, accusing him of failing to see the long-term benefits of the proposals for Scottish football as a whole.
But Gilmour has defended himself, insisting he did not take a parochial approach when deciding which way to vote.
"Let all of them blast their shotguns," he said.
"I'm still firmly of the belief, with all my heart and not letting it rule my head, that what I did at Hampden was the right thing to do.
"I still want to see elements of the reconstruction proposals - like a single league body - implemented, but not at any cost.
"First of all I'll tell the St Mirren supporters later today the reason for doing what the club did at Hampden."