"anyone (from atheist to pagan) can be a Quaker"
I agree. Exactly. That's basically the interpretation of Abdul-Baha too. Reform Bahais don't accept any creed because they're always used to coerce people, for example, the bogus "covenant" or "will and testament" of Haifan Baha'is.
Abdul-Baha publicly delivered his authentic covenant in 1912 in New York. It's
been suppressed ever since his death.
""one religion" (and I believe that is what Schuon and Fox are getting at)."
Fritjof Schuon and other Perennialists are right on target in my personal opinion. A metaphyscian with a universal perspective, Schuon was actually also a Sufi, as Seyyed Hossain Nasr, another Perennialist, explains in his recent book on Islam. I've read several of their books and find them very compatible to what I find in Abdul-Baha's own open, universal vision of the unity of the religions. Nasr describes some of the Perennialists, though, as Muslims, essentially, and that one must become Muslim, in an exclusive sense, to follow the correct spiritual path. Bahai really isn't a secret platform for Islam, except for some Shiite Iranian Baha'is, but is on the journey beyond all the historical pasts toward a universal Form, one we are all seeking together, in my view.
Most presentday Baha'is have little to no knowledge about the early years of Abdul-Baha's actual teachings and interpretation of what he called the Bahai Movement or Cause. That's reflected in some of the comments here. He died in 1921 and it was only then that a fraudulent will and testament was used by his family to take control of the religion, reverting significantly back to their Iranian Shiite heritage, as I've already suggested. Although both Baha'u'llah and Abdul-Baha had repudiated such negative practices in Islam as takfir, denouncing others as infidels, and taqiyya, dissimulation and lying, for the "good of the Faith," Shoghi Effendi brought all that kind of thing back, moving away from universalism to exclusivism, in his pursuit of a Bahai theocracy, which Abdul-Baha had clearly rejected, emphasizing a "spiritual democracy."
If interested, my "A Response to Takfir" was published in a London journal, Religion 38 No 4 2008. Just google the title.
Ruth White was an early Bahai who rejected the unprobated, unauthenticated
will and testament, wrote several books about it, and hired the foremost
forensic researcher of the time at the British Museum to examine the purported will. He declared it a forgery in 1930. google "Dr. C. Ainsworth Mitchell" She's been loathed by Haifan Baha'is ever since...