the issue will eventually emerge that why should one become a Christian at 18 if one can still go to God at 80. The answer is, if one plans his life this way, at 80 (or deathbed), the conversion is false, because the intention is an attempt to cheat God of the obedience he requires.
The crux of the parable at the top of this thread is NOT whether the employer is fair or not, but why should those who got employed in the morning complain, after all they accepted the terms of employment.....