Former Scarlets back Shingler was shown a red card by referee Jerome Garces after 19 minutes for an ugly spear tackle on opposite number Dafydd Hewitt.
The incident came just a matter of weeks after Wales captain Sam Warburton, who was playing his first home game of the season for the Blues, was dismissed for a similar tackle on France wing Vincent Clerc at the World Cup.
And with Heineken Cup organisers European Rugby Cup Limited having signalled an intention to clamp down on dangerous tackles, Shingler appeared to have few grounds for complaint with Garces' decision.
Booth said: "The way the game is being officiated around the tackle means if you are not precise you may pay a heavy price.
"The young lad is devastated. There was no malice in it. He is a young man coming back to Wales, wanting to impress. The guy jumped up and if you are not quite in control of your emotions or are just a little bit off with your timing, that is the outcome.
"The safety of players is paramount. These are big physical people playing a very tough game. But if you are out by a fine margin you can pay a heavy price and we have seen that."
When pressed on whether the referee had made the right decision, Booth added: "Whether I have any complaints is irrelevant - that was the referee's decision."
Despite that setback, which came after the Exiles had made a sluggish start and fallen 10-0 in arrears, the visitors bravely fought back for what could yet prove to be a valuable losing bonus point as full-back Tom Homer kicked six penalties.
And Booth was hugely proud of the character shown by his side, even though they have now suffered back-to-back defeats at the start of their Pool Two campaign.
"I thought the effort was outstanding," he said. "To play 60 minutes with 14 men and give yourselves a chance to win was outstanding. That was brought about by playing cleverly, an enormous forward performance and a great scrum performance.
"We were also finishing stronger then they were with 15 men, but we have to look at how we got ourselves in that situation in the first place."
The groundwork for the Blues' win came from first-half tries by hooker Rhys Thomas and a superb blindside dart by man of the match Lloyd Williams, with Scotland fly-half Dan Parks adding 14 points with his boot.
But the hosts were never able to build on the dominance they enjoyed during the opening quarter, when Irish surrendered possession with alacrity.
And while forwards coach Justin Burnell admitted it was not a great performance, he was more than happy to pick up a second-straight win that sets them up for next month's home and away fixtures against surprise pool leaders Edinburgh.
He said: "When we arrived today [Friday], if someone had said it would not be a great performance but you will win I would have taken that.
"At the start we were very comfortable and had a good intensity like we had in Paris last week. We knew they would try to run and attack us. That was how we trained.
"But in the second half, playing a man down, they kicked everything, threw numbers into the breakdown and slowed our ball down.
"Having said that, I am more than happy with the win."
Burnell also confirmed that he and backs coach Gareth Baber, currently in interim charge of the Blues, have still not had a definitive decision on their futures.
"We will try to keep winning - that is all we can do," he said. "We will continue to put all our focus in to creating a good, professional and winning environment.
"There was a board meeting today [Friday] but when we arrived today my whole focus was on the game and what is in the best interests of the players."