“I don’t understand why people feel threatened by considering the notion that great people they esteem and respect are or were capable of making mistakes or of not addressing a changed circumstance with the keenness they displayed in almost every other circumstance. “
A gadol has a certain siyata dishmaya when he gives psak, and sometimes, ruach hakodesh (there hasn’t been nevua in a long, long time), which stems both from his immersion in Torah and from the fact that the klal relies on him. And there were gedolim who talked about the tragedy to come in Europe (I believe the Chofetz Chaim was one). But perhaps Hashem removed the siyata dishmaya from most of the gedolim when it came to this issue, because that was the desired outcome? Case in point- Hashem withheld nevua from Yaakov Avinu so that he would not know that Yosef was alive in Mitzrayim. History may have been very different had he known that- but the point is that Hashem wanted the shevatim to go down to mitzrayim, and for there to be a shibud of 210 years, and He orchestrated events so that it would happen that way.