A few fans scoffed as the Manchester United chief's name was perused out before start off at Wembley.
Maguire has gotten through a troublesome season with his club however has been a pillar in the England group that arrived at the World Cup semi-finals and Euros last.
"The gathering was a joke, an outright joke," said Southgate.
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A few allies additionally booed Maguire's first touch as England asserted an agreeable triumph because of objectives from Ollie Watkins, Raheem Sterling and Tyrone Mings.
It was Maguire's 42nd appearance for his nation and Southgate said the treatment of the 29-year-old was unsatisfactory.
"I don't have the foggiest idea how it benefits anyone. We're either all in it together or we're not," he added.
"I suppose you asked a couple of them for what good reason they did it they most likely wouldn't have the option to reply. It's crowd mindset. One finish of the ground you have a no-nonsense gathering attempting to get his name sung - it wasn't everyone.
"Players will take a gander at that and think, that could be me. It makes players not have any desire to come. That occurred with John Barnes here, that occurred with Ashley Cole two or multiple times, it occurred with Raheem, presently Harry.
"We want Harry to get along admirably. We won't win a World Cup with a heap of players with three or four covers. That is never occurred throughout the entire existence of the game."
Addressing Sky Sports about Maguire, Southgate added: "The manner in which he has performed for us has been totally remarkable. I don't get it.
"He's in an England shirt and besides the fact that you backing should a player in an England shirt in any case, yet when you've played at the level he has for us - and put the exhibitions in he has - it ought to be all out responsibility behind him.
"His presentation was really perfect truly. He ventured out from the back all around well for the primary objective, was associated with the second one as well. The group are completely joined together. We perceive everybody has troublesome minutes, however he's a top player and he will come through it.
"They are genuine England fans and some are affected by whatever - online entertainment or players that played beforehand who are impacting assessment. The club circumstance is clearly truly challenging, however he's in an England shirt.
"I recollect many years prior a couple of players being booed in an England shirt and it's never been OK to me. Fans ought to continuously get behind their group."
'Harry has been a mammoth for us'
Maguire's partners rushed to show their help for him after the success over Ivory Coast.
Liverpool chief Jordan Henderson said: "I can't get my head around what occurred at Wembley this evening. Harry has been a mammoth for England. Without him, the headway made at the last two competitions could never have been conceivable.
"To be booed at his home arena, for not a great explanation? What have we become? What happened this evening was simply unacceptable. As somebody who needs to win with England I feel lucky to share a changing area with him. We as a whole vibe the equivalent."
Jack Grealish additionally brought up Maguire's part in England's initial two objectives as he referred to the booing as "absurd".
"Harry has been amazing for this nation - the World Cup, the Euros, he has been splendid," said the Manchester City player.
"Our initial two objectives, the first comes from him driving with the ball and the subsequent one comes from him driving a tad. Only one out of every odd focus back has those characteristics."
West Ham midfielder Declan Rice tweeted that those booing were a "complete shame". He said: "Harry Maguire has been inconceivable each and every time he's placed on the England shirt. Outright babble presently it's becoming. Back your own players. Particularly with a significant competition coming up."
Britain skipper and Tottenham striker Harry Kane said: "We've endeavored to remake our association with England fans over the most recent couple of years so to hear Harry Maguire booed at Wembley before start off was definitely not right."
Kane added: "The way that he's been splendid on the pitch and given us generally such countless incredible recollections makes it significantly harder to comprehend. He doesn't merit that gathering. He has full help in the changing room and ought to have something similar from each England fan."
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