...There really isn't any way to makes Orthodox Judaism a Rationalist Judaism. Where does one draw the line? ...It's not that a rationalist Judaism isn't a smashing idea, it's just that it's never going to be compatible with Orthodoxy.
Tzelopchad's argument is one that I have heard from several people (on both sides of the divide) - it was all very well to be rationalist in the 12th century, but rationalism today is simply incompatible with Judaism, so one shouldn't attempt to go on the path of rationalism to any degree. I have three responses to that.
1. Many people believe that acceptance of the tenets of Judaism is rational.
There is heated debate as to whether it is rational to believe in the Divinity of Torah, as well as debate as to what the parameters of this belief actually are. Many people believe that it is indeed rational to possess such belief. This topic is discussed ad infinitum and ad nauseum in other forums. It will not be discussed on this website, because that is not the goal of this website. My goal here is to explore what rationalism meant in the times of the Rishonim, and how those positions are understood today.
2. Many of those who feel that faith is irrational still possess it but feel that the rest of Judaism should be as rational as possible.
Even if one’s attachments to the fundamentals of faith are not rational but rather a conscious leap of faith, a strong case can still be made for saying that one should implement a rationalist approach for the rest of Judaism to the extent possible.
3. Even for those who lack faith, it is beneficial to show that Torah is rational to the extent possible.
There are some people who have tragically lost faith in the Divinity of Torah altogether, but are still members of the Orthodox community, either because it is too difficult for them to leave or because they appreciate the lifestyle. For such people, it is valuable to show how so much of Torah and Judaism makes sense and is beneficial from a purely rational perspective.
I do agree, however, that rationalism has its dangers; I have made that clear on many occasions. However, so does the non-rationalist approach - it leads to obscurantism, and alienates many intelligent people. It's a case of different strokes for different folks.
It's probably a good idea for a post defining rationalism.