Paul Kerr falsely accused John Fagan of raping a nine-year-old boy and posted reams of sexually abusive comments against him and his wife on public Facebook pages, the court heard.
Kerr, 55, sent emails to two police forces threatening to murder Mr Fagan during the course of an 11-month campaign of abuse between January and November 2018, prosecutors claim.
Mr Fagan, who lives with his wife Julie in Canterbury, Kent, has seen Simple Minds more than 300 times and was an active member of an online forum about the band.
The dispute started when Mr Fagan replied to a post on Kerr’s public Facebook page about the band’s new album, the court head.
Mr Kerr had described the new record as “pure s**t”.
Kerr, of Brighton, East Sussex, is charged with two counts of stalking causing fear of violence against the Fagans, and a further charge of stalking against his ex-girlfriend Elizabeth Vanthof.
He appeared at Lewes Crown Court for trial on Wednesday wearing a dark blue fleece.
Best known for their hit single Don’t You (Forget About Me), Simple Minds are the most successful Scottish band of the 1980s.
Prosecutor Jonathan Edwards told the court that Mr Fagan had replied to a post on Kerr’s Facebook page in which Kerr had criticised the band’s new album.
Mr Fagan had commented lamenting the departure of the band’s previous keyboard player and drummer.
It was a few days later that Kerr’s stalking campaign is alleged to have begun, the court heard.
“Mr Kerr, the defendant, posted on his Facebook page that the Fagans had contacted him for help to harm Jim Kerr,” Mr Edwards said.
“That was untrue. Nevertheless it was put out there as a fact by this defendant and then he seemed to escalate things by posting again on his Facebook page that John Fagan was a rapist of a nine-year-old boy.”
The court heard that Kerr took photos from the Fagans’ Facebook pages and reposted them with abusive messages.
Mr Edwards said: “The Fagans were upset, very upset, because what he was posting was untrue but also very fearful because somebody somewhere might believe that stuff that he was posting and take the law into their own hands by trying to harm John or Julie.”
The prosecution alleged that Kerr used fake accounts - including one in the name of his dead mother - to post “sexual abuse and allegations of rape”.
Mr Kerr also threatened to come to Canterbury where the Fagans live to “cripple” Mr Fagan and “drag Julie Fagan by her hair” to a police station, the court heard.
He is also accused of carrying out a stalking campaign against his ex-girlfriend Ms Vanthof between April and November 2018, contacting her at home and at the French university where she worked.
Over the last 42 years, Simple Minds have continued to tour with changing members, though original members Jim Kerr and Charlie Burchill remain.
Their latest record Live In The City Of Angels was released earlier in October and the band plan a major world tour in 2020.
Defence barrister Paul Walker told the court that it is the defence case that Mr Fagan contacted Kerr after being unhappy with the new album.
Mr Walker said: “He invited Mr Kerr to help him destroy Jim Kerr’s career and Paul Kerr reacted to that.
“His reaction on Facebook was not in the manner described by Mr Edwards.
“He wasn’t the author of the particularly vile messages.”
Instead it was the Fagans who created the fake accounts and posted about themselves, Mr Walker told the court.
On the charge relating to Ms Vanthof, he said: “Some of his messages may have been forceful but they do not amount, the defence say, to stalking.”
The trial is expected to last up to five weeks.
The case continues.