Ellen White said that if there is a difference between the Bible and her writings, to go with the Bible... she recognized the Word as the only infallible guide.
Is it possible that while God did indeed use her as a lesser light to illuminate the greater, that there were writings given to test God's people on this point. As you said, there are many that are almost fanatical in there adherance and promotion of certain doctrines that are either not truly supported by the scriptures without a great deal of exegetical acrobatics, or are clearly contrary to the proof text method of scripture.
When people make diet a salvational issue, you have to dismiss it as there is no Biblical evidence for it... therefore those people are making an idol of sister Whites writings above the Word. The Bible does support her idea of temperance in food and drink but not of abstinance.
What is more
You are right the bible does not support her idea of abstinance. - Is she wrong on that?
Now have a closer look at it:
When somebody wants to join the SDA church, they will join the church through baptism - right?
While baptism is biblical indeed, it is not positively clear to me wether baptism can be regarded as a ceremony of joining a church - I could be wrong on this, though. To me it is more like a symbol of rebirth, the washing away of sins - probably still true in regard to SDA baptism - maybe the formal joinging of a church can be regarded as a natural byproduct after being baptised
So, after meeting with adventism one has theoretically two options, join the church after learning or accepting that it is the only true church remaining - the so-called remnant(church) - or deciding to be baptised as a sign of repentance for ones sins and giving their lifes to Jesus. Eventually one goes with the other.
However!!! - and this made me wonder a couple of times - baptism also includes certain baptismal vows. (I dont know too much about adult baptisms in other church, but the SDA certainly has them - I had to go through them myself).
If somebody wants to get baptised they have to go through a set of bible lessons - during which major SDA viewpoints are being explained.
During biblical times - I guess the church was not VERY organized yet it seems to me that accepting Jesus Christ as Lord and Savior was sufficient to be saved - and baptised.
Before one can get baptisez 'into the SDA community', however, one has to agree with a set of SDA believes, the so-called vows. So one is asked if one agrees and I guess after all question have been answered positively one can proceed.
A general question would be: is this biblical at all? I mean, the bible doesnt really mention it (other than accepting Jesus Christ and again correct me if I am wrong on that).
Spontaneously two of these vows I would call rather odd.
One of them is accepting EGW as the spirit of prophecy. Hmmm... this seems a little bit extrabiblical - as we never find egw in the bible - and her given title of spirit of prophecy is based on some interpretion. Furthermore, the bible never speaks about accepting the spirit of prophecy before being baptised. - so at this point the person who wants to get baptised has to accept egw - no matter what - you cannot postpone that point like 'yes, I want to be baptised in the name of the Father, the Son and the Holy Spirit' but egw I am not sure about - maybe never will - does it matter? - I think this will not work - in the SDA you cant have one without the other...
Another vow is the life in abstinance. While it is certainly good not to eat meat and not to drink wine, it is not a necessity. - A choice is given to God's people in the bible. The SDA (through egw I guess) takes away that choice making it a doctrine AND a requirement to proceed further towards baptism. So if somebody does not agree with this - and his disagreement is based on the bible - he is left with two choices, either cancel the whole baptism or agree to those vows but secretly remain confident in ones belief that abstinance is not required and that personal opinion on that topic is chief.
Now the latter point would be very disturbing to me as this would be premeditated lie - a vow that is one never plans on keeping. Thats weird. I understand that people can change their opinions. They made that vow but realized lateron that something was not right with it. But the other way round seems odd to me.
So accepting EGW is a major point in regard to baptism.
How can one accept those things? I mean how can stay true to your bible beliefs and still be baptised into the SDA community? - I guess you cannot!