I don't know why people think Shabir or Naik have memorised the Bible- they quote it just like evangelists quote it or other Muslim debaters would (i.e. memorising the passages that are necessary for debate only, not the entire text). I can't think of a single human being that has memorised the ENTIRE bible and even the memorisation of the Torah itself is rare.
The danger of being misled is great because an average Muslim layman will consider these guys to be scholars of the highest calibre on the basis that they can speak English and quote with verse and chapter number unlike 'these mullahs' who don't. So the most obvious danger is that these people are given a status amongst the laymen that should be reserved for actual scholars instead.
The second being that even in these debates, you'll find people like Shabir making kufr statements. It was in a debate for example, where he denied a hadith of Bukhari that was brought up by the Christian opposing him, with the Christian confused as to why a 'sunni Muslim' was denying the authenticity of a hadith from Bukhari (as he had been correctly told that we believe them all to be authentic). All Shabir said was 'it goes against the Quran' (which it actually didn't). How many laymen would have then been fooled by his ignorance and began to adopt his methodology so that whenever they are shown a hadith that seems to contradict Al Quran, they decide to believe it is a fabrication instead?
The point is, maybe the already religiously inclined may know where he falters but MOST laymen do not and they will be swept up in his ignorance and as such, I CANNOT recommend that anyone watches any of his talks
And I now ask the question- in a Sharia state, do you think he would be allowed to continue his 'preaching' with the Ulema advising that they take the good and leave the bad or would he have been banned or brought before a Qadi to answer for some of his statements (especially ones like the evolution one which is kufr but that is for the Mufti's to explain)?