Different people mean different things by “real” fencing.
For some, “real” fencing is a duel with sharp swords and lives on the line. Other than the fear/courage factor, the primary technical difference here is that with live blades you only need to hit your opponent once, and therefore only require one good move (which explains the prevalence of “secret thrusts” in the bad old days). The sport fencer, by comparison, has to hit his opponent as many as 15 times (even more if the officiating is poor!), and so requires considerably more depth than the duellist. On the other hand, the sport fencer takes many more defensive risks, since he has up to 15 lives to work with.
Some purists will equate “real” fencing with classical fencing, i.e. the prevalent styles of the traditional French and Italian schools of fencing that predominated before electric fencing was popularized. By comparison, modern fencing is more mobile and athletic, while classical fencers were known for their more sophisticated phrasing and bladework.
A few fans of heavy metal think real fencing is only done with big, strong swords, and that light duelling-style weapons are toys. Historically, however, lighter thrusting swords evolved because they were considerably more deadly than heavy cutting weapons. Many masters of the 17th century disliked the new schools of fencing precisely because they were too murderous. However, the light duelling sabres that arose near the end of the 19th Century did lack offensive punch on the cut compared with their more military antecedents. Military sabre fencing required more arm strength, and the use of moulinets.
Lastly, it just seems apparent to some that sport fencing has evolved away from its bloody origins. Technically, this is untrue, at least for the thrusting weapons; the theory, methods, and techniques of fencing have not seen significant innovation since at least the last century. The modern fencer remains well-equipped, skill-wise, to fight a duel. Tactically and psychologically, however, the sport is a vastly different world from the duel. Obviously there is no real danger to getting hit, and with up to 15 hits needed to secure victory, there often isn’t even much figurative danger. In addition, since the quality of a hit (eg. fatal vs. serious wound vs. minor scratch) is immaterial, fencers will naturally prefer an easy “wounding” hit over a difficult “fatal” one, and glancing hits will often win out over strong thrusts.