4. Do other 'mainstream' Christian groups have peculiar beliefs that seem bizarre or cult-like?

Yes, many ‘mainstream’ denominations likewise hold beliefs other Christians might equally characterise as quite bizarre or cult-like.  For example, consider:

·        Roman Catholic worship of Mary and Saints (arguably a form of neo-paganism), the Immaculate Conception of Mary (she was preserved from original sin), the upholding of Sacred Tradition over the Bible, Clerical Celibacy, or belief in Papal Infallibility.

See:http://en.wikipedia.org/wiki/Criticism_of_the_Catholic_Church#Separation_of_church_and_state

·      Reformed views of Perseverance of the Saints (once saved always saved), Election, Predestination and Double Predestination (God chooses who is to go to heaven and who to hell, with little or no real choice by the individual), or Limited Atonement (Jesus did not die for all mankind but only for those elected to be saved).

See: http://en.wikipedia.org/wiki/Predestination_(Calvinism)#Criticisms

·      Evangelical-Pentecostal views on money (Prosperity Gospel), Oneness-Pentecostalism and Jesus-only baptism (rejection of the Trinity in favour of Modalism, albeit by a sizeable minority), Antinomianism (proto-Gnostic beliefs that reject the Ten Commandments), Glossolalia (gibberish ‘speaking tongues’), the Secret Rapture and Dispensationalism (and support for the nation of Israel), and the tendency to follow a single, charismatic (and often authoritarian) leader in one Mega-Church, without any proper accountability.

See: http://en.wikipedia.org/wiki/Prosperity_gospel

And:  http://en.wikipedia.org/wiki/Oneness_Pentecostalism

Also: http://en.wikipedia.org/wiki/10_Commandments#Christianity

Also: http://en.wikipedia.org/wiki/Glossolalia

Also: http://en.wikipedia.org/wiki/Dispensationalism

·       Conservative Christian views (especially amongst ‘Fundamentalists’) generally supporting Legalism and Phariseeism, or adopting a Proof-Text (or Quote-Mining) method of the biblical interpretation, which can lead to absurd results.

See: http://en.wikipedia.org/wiki/Fundamentalist_Christianity

·      Liberal views (especially amongst ‘High-Church’ Anglicans/Episcopalians and Lutherans) supporting Darwinian evolution by natural selection, upholding tradition over scripture, and promotion of Higher-Criticism (rejecting any supernatural aspects of the Bible, including all miracles, and even the literal virgin birth or the resurrection of Jesus Christ).

See: http://en.wikipedia.org/wiki/Liberal_Christianity

To the extent that such groups may claim their beliefs have been misunderstood or misrepresented, or that the conduct of a minority does not properly reflect the whole, this is exactly how Seventh-day Adventists often feel.