My beloved brother (in the Lord) Mark has written a challenging post against the denominational practice of restricting communicant privelege to those who hold a particular view on the mode of Christ's presence in the Sacrament.
I wish I could go into the subject in more detail, but I was raised in a "church" that made a very big deal about who could or could not partake of the Supper. The Plymouth Brethren began in the early 1800's originally as merely informal meetings of Christians from various ecclesial affiliations to "break bread" together and rejoice in a common faith and salvation that transcended organizational boundaries.
This original ecumenical principle began to fade as the Brethren movement evolved into the Brethren Ekklesia or "Gathered Assembly." In order to justify the creation of a new denomination (in fact--if not in name), John Nelson Darby (JND) argued that any group that separated itself from the contaminations of "moral evil" (i.e., immorality) and "ecclesiastical evil" (i.e., doctrinal error) had been ipso facto gathered by the Spirit unto Christ alone. This, as I understand it, is the theoretical origin of non-denominationalism.
Obviously, JND thought his party (one of many Brethren groups that remained after several schisms in his lifetime and beyond) had sufficiently purified itself from moral and ecclesiastical evil. This Gathered Assembly is still understood by strict Brethren today to constitute THE TESTIMONY to the truth of the "one body" of Christ on earth. Of course, they all differ among themselves as to which Brethren sect actually testifies to this Truth, but they are all certain such a Testimony exists!
My response to all this pablum is that the Lord Jesus Christ is perfectly capable of purifying his own Supper so that unbelievers and sinners will not defile God's people if perchance they unworthily partake of the blessed sacrament.
For more info on JND & the Brethren, readers can check out William Blair Neatby's A History of the Plymouth Brethren.