Careful... Many of the anti Mormons here on FR are Christians who do not believe that baptism by water is nessisary.
If one wants to be considered a Christian in anything other than the narrowest of circles, they need to submit themslves to the Christian rite of initiation, i.e., water baptism with the proper Trinitarian formula.
Since human beaings cannot look on the heart, they must examine externals to validate a testimony. Denial of water baptism calls this testimony into question. That is what cults are made of.