Both those posts are the result of fallacious thinking.

1) The fact that helmets can contribute to injury does not mean they cannot prevent injury.

2) If a bicycle helmet is adequate protection against thing like getting hit by a car traveling at high speed (which is the argument being addressed in the post you quoted) then there doesn't seem to be any need for larger, heavier helmets. Practicality never entered the discussion so is essentially a strawman.