If one really wants to analyze any new idea truly critically, one should prefer to read about it. There just is a big or even crucial difference with reading and watching or listening a live presentation. When one reads something instead of watching or listening, one can decide the pace and rhythm of receiving the information wholly by oneself.
This difference is increased by the difference in the amount of information received. Watching a person speaking will inevitably suck in more of our brain-capacity than just reading. Following the physical activity of the speaker will inevitably draw more attention from all of our senses.

Similarly, underlying emotions can be transmitted by a live performer in a way that a writer cannot. All studies show that, for example, television is a much stronger media than written word in all meanings of the word. However, this piece is about analyzing factual information and ideas and this respect purely emotional input coming from a live performer can, in fact, derail the process.
One can simply remain more of a master of one's own mind when reading. This is the case, even if also when reading one lets the written ideas impact one's mind. A reader simply has much more intellectual freedom than a listener. When one listens and watches a speaker, the speaker can easily get a very strong hold on how one's mind does process his message. Most of all critical thinking can be much more difficult when one is listening to somebody who is presenting his or her ideas in a live situation.

Folio 14 recto of the 5th century Vergilius Romanus contains an author portrait of Virgil. Note the bookcase (capsa), reading stand and the text written without word spacing in rustic capitals. - Wikipedia

The main thing is that when one reads, one can proceed wholly at one's own pace. When one stumbles into an idea that needs more thinking, one can always pause completely. When following speeches, lectures or television shows new text just keeps coming in whatever one does. One just cannot control the flow of it.
This all just might be because of the way how the human brain is wired. The brain will quite automatically concentrate on the new stuff coming in. Analysis of what one has already heard is much more difficult during this process. It is not impossible to process and analyze the incoming spoken words also in real time. However, it just might be much more difficult, and the difference can be even huge at times.

Old wisdom is that if one really wants to convince somebody one will never have the same effect by sending a letter as with a phone call or a personal contact. Of course, the personality is very much at play here also, but also the simple fact that a reader simply has more mental elbow-room to analyze the text and its ideas, but also writers motives and reasoning.
When one is in a face-to-face-situation delivering the very same thing, the listener just might have much less room for his own thinking while he is concentrating on listening. This may also be a major reason why all religions want to gather their followers to regular personal gatherings where the same central ideas of the religion are presented time after time in spoken form. Reading the holy texts by oneself just is not enough, as the critical part of the mind has too much room to move around while reading.

The keeping up a strong faith-based religious conviction just might require constant strengthening in a situation when you must go with the flow of the words. Written text is necessarily more impersonal and will always have less straight emotional impact than spoken word. Old wisdom is that written word relies more on the rational part of the mind and spoken word is much more emotional.
An important factor could also be that when reading one is much more the master of one's own mind. One can decide how one will consume the text at hand and in what kind of parcels one will do it. You just have more time to think about the individual arguments and their real merits.
When one is listening to somebody, the speaker gains much more power over listeners mind. By getting to choose the pace and rhythm in which things are presented, the speaker can just manipulate one's mind-process to a much greater degree than is ever possible when one is using the written word.

(This piece was completely refurbished on 6th 3rd of January, 2012)