D'Arcy and Monk have been ordered to leave London as soon as their events at the Olympics finish and have been banned from using social media during the Games.
The punishment for posting online photos of themselves posing with high-powered guns at a US rifle range was branded heavy handed by many members of the public and some swimmers.
But Coates, who ordered D'Arcy off the 2008 Olympic team for assaulting former swimmer Simon Cowley, backed the measures taken by chef de mission Nick Green and his selection committee.
"Our selectors made a value-judgment and I can understand that not everyone is going to agree," the Australian Olympic Committee (AOC) president said on Friday.
"Not everyone agreed when I put him (D'Arcy) off the team last time.
"I know that Swimming (Australia) when they sat down with them, said 'you've got to understand that in the eyes of our sponsors and the Australian Sports Commission - and they are 50-year-old eyes, not 20 year-old eyes - they did view what you did seriously'.
"You've got to put all that in perspective. But the decision has been taken - and I support it."
He said the AOC's social media policy had been in place for more than a year and that athletes should be well aware of what was expected of them.
"We've been lecturing athletes on how they have to be careful with the use of social media during the Games and that hasn't changed," he said, adding cycling's decision to ban social media when trackside during the Olympics was one of the more recent changes the team had been made aware of.
Coates also said he's looking forward to catching up with triple Olympic gold medallist Grant Hackett following the former swimmer's split with his wife earlier this year.
Hackett has also lost several contracts amid allegations of alcohol-fuelled violent incidents, including trashing their Melbourne penthouse.
"We've been communicating by email he sent a number of us a thank you," Coates said.
"I'm just looking forward to catching up with him - it's a personal matter."