Baptism is the one sacrament necessary for salvation for all men. It is the only sacrament that every person on earth, above the age of reason, can validly administer. It is the "easiest" sacrament to confect. An unbaptized man would need one other person, a handful of water, and about 5 seconds of time to receive the Sacrament of Baptism. The administer needs to know only, I believe, 11 Latin words for the proper form, or several more in English, probably more or less the same in other languages.
Water is the the most abundant matter on the surface of the Earth, covering over 70% of it. Water is absolutely necessary for natural life. Wherever man is, he needs water. He cannot live more than several days without water. He will catch rain, melt snow and ice, collect the dew on leaves to obtain water. Our Lord's words seem to indicate that it is also absolutely necessary for supernatural life (John 3:5)
Not really a theological argument..I just find it hard to believe that anyone properly disposed to receive the Sacrament and desiring it would not once in their life have the opportunity and means to receive it.