And he that doubteth is damned if he eat, because [he eateth] not of faith: for whatsoever [is] not of faith is sin.
Note 18 at Ro 14:23: The Greek word that was translated "damned" here is "KATAKRINO," and it means "to judge against, i.e. sentence" (Strong's Concordance). This differs from the Greek word "KRINO" that is used in 2Th 2:12 to designate eternal damnation. KATAKRINO, as used in this verse, actually means, "to condemn" (Vine's Expository Dictionary), and it was translated as "condemn" and "condemned" fifteen times in the New Testament. In contrast, KRINO was only translated as "condemn" once (Joh 3:17), "condemned" twice (Joh 3:18), and "condemning" once (Ac 13:27).
Therefore, this verse is not saying that Christians who do something with defiled consciences are eternally damned. Paul was stating that Christians who violate their consciences are going to come under condemnation.
Note 19 at Ro 14:23: This verse provides us with a definition of sin that is applicable to all people of all cultures and different religious backgrounds. Any action is sin for us if we don't have faith in its correctness. Thus, until we can settle our doubts, we aren't to do it. This provides an infallible system for determining right and wrong for any individual.