Thompson's reign at Sheffield ended on Monday after a poor start to the season. It was a victory for a section of Steelers fans who he repeatedly called for his resignation.
Finnerty, coach at Elite League rivals Manchester Storm, believes Thompson was "thrown to the wolves."Â He regards Thompson as "one of the best coaches this league has seen or ever will see.
"I was shocked when I heard, it was a sad day for British ice hockey, the end of a great coach and for me a mentor, after just a handful of games.Â He'd been lambasted like he was the devil on social media after a few games in a 60-game season. Some of the stuff I see is disgusting.
"Hockey coaches here aren't like Â£2m a year football managers, we don't retire to our beach house and become a pundit, we get a normal living. We have mortgages and families.
'But Thommo got a lot of stick mainly because he was at Sheffield Steelers, where the expectation is that they will win every game."
Finnerty will always be indebted to Thompson - in 2011 he signed for him as a player at Coventry Blaze butÂ was then invited to become coach at Steelers. Thompson waived his contract to put him on the ladder.
"He stood up for me because he knew it was a great opportunity and after that, he became a mentor.'
"Later, he went to Sheffield a club which everybody wanted to be like, a Man United of hockey where there is a demand for success in every game. Every player there is expected to be of a certain pedigree and sometimes it doesn't always work out."
Thompson was vilified by some for failings in recruitment and his technical abilities.
"People have a go at him signing the Rupert brothers. I also did my research on them and if I could haveÂ afforded them I would have hired them.
"But sometimes players turn up out of shape - and that's on them, not the coach. They were expecting to play in the ECHL which started later. But no club in our league can send their conditioning coach overseas to check on them. It's on the players.
"As for tactics, he was a good as anybody. But it's always the coach's fault if a team loses. You can outshoot a team 65-12 and lose 2-1...and it's the coach's fault.
"All of Thommo's teams played hard and worked hard. He has a tremendous desire to win. There's nobody with his experience.
'It's easy for people to say a coach is out-dated - people used to say my style of hockey was just dump and chase. Fans have the right to criticise even if they don't know all that goes on.
'I don't go with the fans who went head-hunting his job - they cannot tell me what he was about."
Physically, Thompson looked like he was starting to feel the pressure, towards the end of his Steelers' career.
"That's what you look like when you care, when you give a ****" said Finnerty.
"I'd like to go to that parade when you are given a league title after just handful of games.
"Him leaving in this way will not sit well with the other coaches in the league; he's been thrown to the wolves."
Finnerty, who says he has a lot of respect for the Smith family that owns the Steelers, does not expect Sheffield will have any difficulty filling Thompson's chair.
"They will get a ton of resumes" he said. "There will be some good coaches available, but this is not an easy league to comeÂ into..."