In a crash, most likely, everyone will die anyway, regardless of whether they were in a secure seat or not.
That's not true. Most accidents do have survivors. Look at the miracle on the Hudson. Look at the accident in Toronto where the plane went off the runway and caught fire, all got out. Look at the one in the cornfield in Iowa, over half survived.
To add to that: Studies have found that 90%+ of airline accidents are survivable. For a slightly-dated NTSB report on this subject, see
http://www.ntsb.gov/doclib/safetystudies/SR0101.pdf. An excerpt:
Because a public perception is that aviation accidents are not survivable, the Safety Board also examined the proportion of occupants who survived in each accident for the period 1983 through 2000. Contrary to public perception, the most likely outcome of an accident is that most people survive. In 528 of the 568 accidents (93.0 percent), more than 80 percent of the occupants survived (figure 3). Accidents that result in complete or near complete loss of life, such as TWA flight 800, account for a small percentage of all accidents. Only 34 of the 568 accidents (5.9 percent) resulted in fewer than 20 percent of the occupants surviving.
A lapbaby could be a projectile in an accident or even severe turbulance.
Again, to add to that - the National Transportation Safety Board's report on the crash of United 232 in Sioux City, Iowa on July 19, 1989 recounted:
There were four in-lap occupants onboard flight 232. Three of them were under 24 months, and one was 26 months old. During the preparations for the emergency landing, parents were instructed to place their "infants" on the floor and to hold them there when the parent assumed the protective brace position. The four in-lap occupants were held on the floor by adults who occupied seats 11F, 12B, 14J and 22E.
The woman in 14J stated that her son "flew up in the air" upon impact but that she was able to grab him and hold onto him. Details of what happened to the 26-month-old child at 12B during the impact sequence are not known, but he sustained minor injuries. The mother of the 11-month-old girl at 11F said that she had problems placing and keeping her daughter on the floor because she was screaming and trying to stand up. The mother of the 23-month-old at 22E was worried about her son's position. She kept asking the flight attendants for more specific instructions about the brace position and her "special situation with a child on the floor." The mothers of the infants in seats 11F and 22E were unable to hold onto their infants and were unable to find them after the airplane impacted the ground. The infant originally located at 11F was rescued from the fuselage by a passenger who heard her cries and reentered the fuselage. The infant held on the floor in front of seat 22E died of asphyxia secondary to smoke inhalation.
While the report doesn't make a point of it, note that the 26-month-old child was not eligible to be lap-carried (and most airlines now will ask for a birth certificate to make sure that a lap infant is under 2 years old).