"Eastern Orthodoxy coming back into full Communion with the West would provide the Western branch of the Catholic Church (for Eastern Orthodoxy is also the Catholic Church, properly understood) with a lifeline."
This is one way of looking at it, however, I think it is not a good motivation for seeking unity and it is looking at it from the perspective of what would be good for the West - not for the East. This approach would be effectively using other Christians as a means to an end i.e. using them as a means to sort out the problems which we have the responsibility to put right. If we are to seek unity, then our motivation should arise from our love for God and love for our estranged brethren.
"Now, I don't really believe that the Western Church is collapsing."
It will not collapse terminally, but it will continue (in the developed countries) to contract dramatically under the weight of our sin and loss of faith. As the Pope himself has said there is a "silent apostasy" going on - sometimes not so silent. However God will preserve His faithful remnant.
"It is very politically and emotionally satisfying to cut the lines and let the West drift onto the rocks....That is what you have proposed. It is wrong."
Obviously I was speaking hypothetically as I am not an E.O. and I cannot pretend to be able to think as such. However there are many problem areas of deep division which I fear will still take decades or centuries to overcome.
Not least of which is the fact that many of them do not trust our motives and they do not trust Rome. This isn't just in their hierarchies, but it runs deep down to the grass roots.
Many of their Churches have only just come out from under the Communist yoke of oppression, and many are still under the repressive attentions of Islam. They need space to regain their confidence as Churches and communities without the fear that they are being lured back into another situation of oppression. This is why IMHO that the Pope ought to leave Patriarch Alexy alone, and give his Church the room to make the first approach if ever they feel ready.
Another factor which complicates this on the psychological/spiritual level is that the E.O. system of autocephaly has engendered a very different sentiment to the other Churches than we generally experience as Catholics. As Catholics we tend to have a very highly developed "sensus Catholicus": we relate to Rome as the centre of unity, we have a strong sense of the Church Universal, to seek unity with other Christians is obviously a good thing.
In comparison, in E.O. there is a much greater sense of sufficiency of the local Church which is based usually on ethnic and/or cultural lines. Consequently the sensus Catholicus is less developed and the desire for unity not such an imperative.
I grant you your point re the sensus Catholicus, especially the part about being Rome centric. In the Eastern Church, we don't speak about "unity", but rather "communion" because so far as we perceive things, the fullness of the Church is, as St. Ignatius of Antioch tells us, where the bishop is. This so because the bishop stands in the place of Christ at the Eucharist and at every Eucharist is the fullness of the Church. The Eastern Church views the Church as a Eucharistic society. Organization is necessary, but that takes a back seat to the inner, sacramental life of the Church. Metropolitans and Patriarchs, while due precedence in honor and administratively may have more to do, yet they are no more bishops than any other, their "flock" no more the Church than that of any other bishop. The Eastern Church, traditionally, is organized along ethnic lines, though it has also been organized along regional lines as with the Patriarch of Alexandria or the EP's claim to jurisdiction over "barbarian lands". Because the fullness of the Church is where each of the bishops, individually, is, central unity isn't the point with us (nor for that matter is ethnicity). For us, communion, determined by shared Faith, praxis as it reflects the Faith and ecclesiology, is what describes the relationships among the Orthodox Churches. Within each "national church" the Church acts in Synods of hierarchs and occasionally (outside of some places like America, among others where they are more common)in Councils of the national church. The highest authority of the Eastern Church would be a Great Council of all the national (or regional) churches in communion with each other. The decisions of such a Council would be binding on everyone. Your unity is visible and at least traditionally quite tangible. Our communion is more mystical since as we see it, the fullness of the Church has been preserved without the necessity of a central, universal authority.