The obvious counterargument is, "You're RIGHT! that's why Blue Whales do not exist." Typically, you get back that they spend their time in the water, which of course, Sauropods did for large parts of their life cycle as well.
It aint easy being huge. But it's far from impossible.
Fred, there is ZERO evidence that sauropods spent any time in water at all. . . zip, none, nada. . . except their large size. That is a logical fallacy called begging the question. They show no adaptation to water, their fossils are not found in watery climate zones, and the design of the sauropod feet is in no way adapted to walking on mud. The thought they wallowed in swamps was abandoned in the 1920s.