Lutherans follow the Bible along with the writings of Luther (Large Catechism, Small Catechism, etc). Reformed and Presbyterians follow the Bible along with the writings of John Calvin. Etc.
Protestantism was created out of the pronouncement of the absolute literal truth and unerring fact of the Bible.
Where I live, the largest protestant (and “national”) church is protestant - the church of scotland.
This is Presbyterian, a denomination which has “scripture alone” as its doctine. And yet, in 2012, the Church of Scotland:
- permits divorce and remarriage of its members (against what the bible says)
- does not stone adulterers to death (against what the bible says)
- has openly homosexual clergy who live with their partners (against what the bible says)
- permits members to eat shellfish (against what the bible says)
- permits members to wear garments of mixed fibers (against what the bible says)
to give a few brief examples, off the top of my head.
So it is easy and quick to see both that the “bible alone” stance is invalid, (surely reason and tradition must also feature, as per Catholicism), and that (at least some) protestantism does not “do what it says in the tin”.
If you look at the recent (last 60 years or so) history of protestantism - with the Church of Scotland again being a good example - you see that it is a history of gradually abandoning their principles and making accommodation after accommodation with the whims of the secular world.
They have done this (accepting divorce, homosexuality etc) to try and “remain relevant” but in fact they only advertise their own irrelevance, as shown by their collapsing numbers. They have reached a stage where membership of (one of) their organisation offers nothing which is not already available in the secular world.
A further lack of basic credibility is highlighted by the fact that opinion can veer wildly between protestant parishes, due to the lack of a centralised guiding authority (Pope). For example, one Church of Scotland parish happily voted in an openly gay (and sexually active) minister, while other parishes were outraged by this and some have left the C of S over it.
Therefore it is my opinion that mainline protestantism is today most groups of people who are attempting to be Christian, but they are not ‘following the Bible alone’ - they are largely “suiting themselves” morally, as they are unable to comprehensively reject secular morality in favour of what they themselves claim to be divine and infallible (the Bible).