By Gene Cherry EUGENE, Oregon (Reuters) - Justin Gatlin skipped along the track during his workout, sunglasses on, seemingly without a care in the world. And why not? The 33-year-old American, who has served two doping bans, rocketed to a lifetime best of 9.74 seconds in the 100 metres on May 15 and last weekend equalled his fastest ever 200m (19.68) at the Prefontaine Classic. Adoring fans kept him busy signing autographs for nearly an hour after his 200m win, but Gatlin's popularity is far from universal. Calls for the sprinter to be kicked out of the sport due his doping suspensions, one of which was for four years, have been widespread, coming from fellow athletes, social media and newspaper columns. "Justin Gatlin not only threatens Usain Bolt - he threatens athletics," blazed a recent British newspaper headline. The criticism, though, seems to have done little to deter Gatlin, who is looking for another fast 100 in Rome on Thursday. "I have cut that emotional rope off and let that ship sail," he told Reuters when asked about the uproar. Maybe, maybe not. Gatlin became noticeably testy at a news conference before the race. A reporter had asked for details on his 2006 positive test for the banned steroid testosterone, while another wanted to know his thoughts on a Norwegian study of mice that indicated the use of steroids could have long-term benefits. Gatlin has always maintained that a massage therapist rubbing a steroid-laced cream on his legs caused his positive test, though many doubt that explanation. His recent times have also left some in disbelief. Only four men have run faster in the 100m, and just seven in the 200m, despite the earliness of the season and the lateness of Gatlin's career. "People are going to have what they want to talk about, what they want to write about," the 2004 Olympic and 2005 world champion at 100m said in the interview. "If my competitors are OK with running against me. If he (world record holder Bolt) is OK with me running fast times and pushing him to be a better athlete, I really don't care what the world thinks." NO POPULARITY CONTEST Were it a popularity contest, things might be different. "But I am not trying to win over my naysayers," Gatlin said. "That's not my point in being in track and field. "I don't want to leave the sport saying I could have run faster. I just want to be tapped out, like I gave it my all," Gatlin said. "I think a lot of people who have the opportunity, and who are capable of running 9.7, probably hold back because they don't want to run so fast early and get the notion of being burned out." Eligible under athletics and world anti-doping rules to return in 2010 after his four-year ban, Gatlin has shown steady improvement. He won medals behind Bolt in both the 2012 Olympics (bronze) and 2013 world championships (silver). But it was last year when the uproar over his participation reached full steam. With Bolt injured, the American dominated sprinting, going undefeated in both the 100 and 200. This season he has raised more eyebrows and there is the very real possibility he could threaten Bolt's dominance when the two meet at August's world championships in Beijing. Bolt, whom Gatlin calls "the greatest in the world at what he does," has started slowly but that will change, the American said. "He knows what it takes to be at the top of his game," said Gatlin. "When the world championships come around I am expecting to go out there and see the Bolt of old." (Editing by Peter Rutherford)