CM Punk should NEVER fight again ... according to Mike Jackson, who says if not for the mercy he showed, Punk could've been badly hurt Saturday night.
TMZ Sports talked to Jackson about his UFC 225 fight against Punk ... and, while MJ says Punk is a tough MF'er ... he also says real-life fighting ain't for him.
FYI -- CM went the distance in the fight ... but was thoroughly dominated.
"It's not even a knock on the man and his skills. It's all about his safety. We're in a sport where you're trying to incapacitate someone," Jackson says, "It's a dangerous sport. People's lives, health is on the line."
Jackson goes on to say ... "I never wanted to hurt the guy. I just wanted to beat him up a little bit, so he knows not to do this no more"
"The Truth" also sent a message to Dana White -- who was pissed 'cause he thought MJ was showboating during the fight.
"If you're sitting on the outside watching, I understand what it may have looked like. But, that's not what I was doing. I'm not a showboater. I'm not a taunter."