In the case of the Quran/Islam it also makes an extra claim which makes it more dangerous - that it is "the final word", Muhammad being the final prophet.
How is this dangerous?
Muhammad (pbuh) had the same message as Jesus, as Moses, and those before them (as we Muslims believe it - these guys are Prophets for us as well). Only difference is their works were corrupted and lost forever so God had to send another Messenger. But idk how it being the last is 'dangerous'.
The Bible isn't always claimed to be perfect or even directly from God completely. There are wide disputes in such claims within Christianity. And I can make a strong case w.r.t Buddhism as well, but anyways.
Weird Christians they are then, if they believe the book of God isn't perfect.