Sidney Rigdon on Other Christians

I found this remark by Sidney Rigdon (1793-1876; served in Joseph Smith's First Presidency from 1832-1844) while looking aimlessly through the Latter Day Saints' Messenger and Advocate, and knew I ought to mark it down for further consideration:

The Savior of the world, of whom it was said, that he was the brightness of the Father's glory, and the express image of his person, was called by all other sects in religion in his day, the beelzebub, the very prince of devils. So little did they know of either the Father or the Son, that when the express image of the Father was before them, in the person of the Son, they supposed that it was the prince of devils himself. Those sects and parties knew as much of God, as do the sects of this day. The Presbyterians, the Methodists, the Episcopalians, the Baptist, and the Campbellites, know as little of the Father and the Son, as did the Pharisees and Saducees of the Savior's day, and the Savior has said, that, "If they have called the Master beelzebub, so will they call the servant also." (Sidney Rigdon, in Latter Day Saints' Messenger and Advocate [March 1837] 3:478-479)

It would seem that if one makes sweeping claims that, say, Methodists don't know the Father or the Son even a slight bit better than the Pharisees did, one must therefore be denying that Methodists are true worshippers of God at all, and therefore cannot be Christians. What are your thoughts on this? For Latter-day Saint readers, would you stand by Rigdon's remarks today?