One of the biggest opponents of categorizing the state of Israel as the beginning of the redemption was the Lubavitcher Rebbe Zt"l. In a wonderful pamphlet called "HaMedina HaYehudit" written by Rabbi Yaakov Moshe Bergman, the Rebbe's position is analyzed and challenged from earlier sources. I will bring parts of this pamphlet here in loose translation:
The Rebbe held that perceiving the state as a stage in the redemption goes against an explicit Halacha in the Rambam. The Rebbe repeated this idea in many different forums at many different times (עיתון כפר חב"ד, גליון 1012 ערב ר"ה התשס"ג עמ' 84-94).
One of the Rebbe's main arguments was that the Rambam set up the explicit order of the Geula in Hilchot Melachim. It seems from a simple reading of the Rambam that the first stage of the redemption must be the appointment of a king. Without a messianic king, we can not say that the redemption has begun. Here are the words of the Rebbe Zt"l in one of his letters (אגרות קודש, כרך טז, עמ' רטז):
Here are the words of our great teacher, the Rambam, in his book Mishne Torah in regards to the return to Zion:
a. In the future, the messianic king will rise and restore the Davidic monarchy to its former state, and build the temple, and ingather the exiles ...
...
d. And if a king from the house of David would rise who is learned in Torah and performs Mitzvot like his ancestor David, according to the written and oral Torah. And this king will force all of Israel to go in [the Torah's] path and will also fight Israel's wars, then this person is potentially the Mashiach. If he succeeded and built the Temple and ingathered the exiles then he is definitely Mashiach.
The preciseness of the Rambam's language in Mishne Torah is well known as is the preciseness in the order of his words. Thus, the order of the redemption according to the ruling of the Torah is: First a king will rise and restore the monarchy, then build the Temple, and the gather the exiles. ...
There are several answers to the Rebbe's arguments. I will bring two.
Can we pasken like the Rambam without an explicit source in Chazal?
The Rosh writes regarding the Rambam's mishne Torah (שו"ת הרא"ש כלל לא ס' ט):
Mistaken are the ones who derive rulings from the Rambam when they are not knowledgeable in Gemara, to see from where [the Rambam] learned his rulings ... thus a person should not rely on his reading of the Rambam when it comes to psak unless he can find support in the Gemara.
Many poskim quote this Rosh as halacha (ריב"ש ס' מד, יד מלאכי כלל כ. הסמ"ע בהקדמתו לשו"ע חו"מ). There is an opposing view that can be found in the Shoel VeNishal (שו"ת שואל ונשאל ח"ה יו"ד ס' א) who says the halacha is not like the Rosh. He agrees however that when the din is not explicit in the Rambam but must be learned through the exactness of the Rambam's words, that we do not rule in accordance with the Rambam unless we have a source in the Gemara. The Rebbe's reading of the Rambam requires a careful reading of the Rambam and therefore needs a source in Chazal in order to be established as Halacha.
I do not know of any source in either Talmud for the Rebbe's understanding of the redemption process. On the contrary, such an understanding goes against several sources in the Gemara:
1. The Gemara in Megilla (17b) describes the stages of the Geula. This Gemara was also brought down in a halachic source (בית יוסף או"ח ריח). According to the Gemara, the redemption begins with wars, then flowering of the land and the ingathering of the exiles and only in the end of this process does the Mashiach come. The Gemara is explicit that wars precede the coming of Mashiach and calls these wars "Atchalta DeGeula".
2. The Gemara in Sanhedrin (98) gives signs to recognize the era of the redemption. The signs do not include a king but rather the flowering of the land.
3. The Yerushalmi in Maaser Sheni (פרק ה) says: "Rabbi Aha says, that is to say that the building of the Temple will precede the monarchy of David." And on this Yerushalmi wrote the Shaagat Aryeh: "These words of the sages are trustworthy for us. May the Merciful One cause us to merit the building of the Temple and the era of Mashiach."
4. The Tosefot Yom Tov (מעשר שני ה:ב) wrote: "The Temple will be built before the monarchy of David is established and we will find that until the Monarchy of David, our enemies will still have a little power over us, just like it was in the time of the second Temple.
Thus, without any clear indication in the Talmud for the Rambam's psak we must follow the Rosh and conclude that the halacha is not like the Rambam in this case.
Is this the actual pshat in the words of the Rambam?
Everything we have said so far assumes that the Rebbe's understanding is the only one there is in the Rambam. It is not clear however that the Rambam meant the passage at hand to be a definitive halacha. In chapter 12 of Melachim (הלכה ה), the Rambam writes the following:
All these matters and things related to them, no one will know until they occur. These are hidden concepts from the prophets and even the sages have no clear tradition regarding these issues except through there textual methodologies. Because of this [the sages] argue regarding these issues. In any case, the order and specifics of these events are not of critical importance to our belief system (עיקר בדת).
While the Rebbe's understanding is of course a legitimate one that has is own sources, mainly in later midrashim and in the Zohar. It must be understood that there is no Halachic necessity to believe in this particular type of redemption. I will end with the words of the Chafetz Chaim written to his son in the year 5656 when there was a great awakening among our nation regarding the return to the land:
ואפשר שהוא אתחלתא דקיבוץ גלויות, הוא קודם ביאת המשיח
It could be that this is the beginning of the ingathering of the exiles which precedes the coming of Mashiach.
