I flew with my first 2 as lap babies many many times. Then when 3rd was 5 mos old we lapped with him to Calif. On our return flight we faced an emergency landing situation at O'Hare (with ambulances and fire engines waiting for us on the runway). It was terrifying - there is NOWHERE safe for the baby to go. Back then they made you put the baby on the floor between your feet
I understand they will now let you hold the baby - but if we had hit any harder than we did, I could have crushed him - or lost hold on impact. Stewardess said as we all (fortunately with no one seriously hurt) deplaned "that's why lap babies have been found in the overhead luggage compartments in crashes". Only happened to me once in 40 years of flying - many hundreds of flights have been uneventful (I still love to fly) - but once was enough for me!! I never fly without a seat (and carseat for infants) for everyone in my family - not worth the risk. So to me the final decision is a risk assessment and what you feel comfortable with/ can live with if you're unlucky. The $ saved would never compensate for an injured child for me.