In an action-packed ninth stage on Sunday, Fabio Aru attacked Chris Froome six kilometres from the top of the key climb of the day as the race leader raised his arm for assistance, later saying he had a mechanical problem.
Froome and some others believe the unwritten rules of the peloton stipulate that you don't attack the yellow jersey if he is not in capacity to respond.
LeMond, as well as several other former riders, strongly disagree.
"There should never be an unwritten rule that you should stop. Sponsors are paying millions of dollars to get performances," LeMond said.
"If you're riding along at 40kph and you see the yellow jersey stops to urinate you don't attack, if he crashes and you're not racing fast, you don't attack.
"If the race is on, it does not matter what happens to the yellow jersey, he's got a team and that's what a team is for," added the American, who won the Tour in 1986, 1989 and 1990.
After Aru made his move, he was followed by most of the main contenders while Froome was changing bike, but Australian Richie Porte and Ireland's Dan Martin talked to the Italian to slow him down.
Controversy as Aru and Quintana attack after Froome is forced to swap bike
BMC Racing leader Porte later abandoned after crashing in the final descent.
Aru did not follow up on his attack and Froome caught them -- ending the stage in third place and collecting four seconds in time bonuses.
One team, however, went on ahead. AG2R-La Mondiale took all risks in the descents to set up Romain Bardet for the stage win and it almost paid off, last year's runner-up being caught only two kilometres from the finish line.
"What AG2R did was the best thing I'd seen in a long time," said LeMond.
"There's no team like that on the Tour, they are happy with second place. And BMC, who are they riding for? Are they racing for Richie Porte or for Froome?
"These guys should perform for their sponsor. I would ask for some money back," he added.
LeMond believes Sky have too big of an influence on the rest of the peloton.
"Sky have been doing that for a couple of years. They come up and slow people down," he explained. "Remember that stage to the Mont Ventoux (last year)."
Stage 12 highlights: Froome still in yellow after Mont Ventoux chaos
In 2016, Froome stopped to wait for three team mates who had crashed in a descent ahead of the climb up to the Mont Ventoux, and the rest of the peloton slowed down to wait on them.
"The riders have lost their ability to race," said LeMond.