Here are some more of my musings on this topic.  Perhaps they will be of use to you.  I give them to you in compact form.

IF you think the congregation IS the final judicatory
     AND you think that believer baptism is both certainly TRUE and CLEARLY IMPORTANT,

          then you will require belief in believers baptism for membership in the congregation.  Weaken any one of those three ideas (congregationalism; certainty of truth of believers baptism; importance or significance of believers baptism) then it will cease to be regarded as an appropriate requirement for membership. 

So, among those who could reject this as a requirement for membership would be those who are

            *committed congregationalists and baptists, but who simply think the issue is not really very significant;

            *committed congregationalists who agree that baptism is important, but are not quite certain of the rejection of infant baptism or the truth of believer baptism;

            *committed baptists who understand the importance of baptism in the church, and yet don’t conclude that the authority in the church should necessarily rest with the congregation as a whole.
FURTHER QUESTIONS:

            Will you discipline people for not coming to the Lord’s Table?

            Will you discipline people for not being baptized?

            Doesn’t a church have to define what is and is not coming to the table, and being baptized?