The thing with human exhalation is that this CO2 comes from the food we consume and gets captured again when food is produced thus having netzero influence on the actual CO2 in the atmosphere. Same basically applies to biodiesel. Of course that ignores energy spent to produce crops and other issues like fertilizer.
The problem is the fossil fuel that is concentrated carbon from millions of years of plants and now just adds to the CO2 in the atmosphere without a corresponding mechanism to take it out again.
If we create gasoline by capturing CO2 from the atmosphere there isn't a CO2 problem with using it for fuel. Processes exist, but all have some (major) inefficiency issues.
The problem is the fossil fuel that is concentrated carbon from millions of years of plants and now just adds to the CO2 in the atmosphere without a corresponding mechanism to take it out again.
If we create gasoline by capturing CO2 from the atmosphere there isn't a CO2 problem with using it for fuel. Processes exist, but all have some (major) inefficiency issues.