The reason for this is every sound has its own frequency & wavelength which doesn't match with any other sound. So ,our great Rishis already gave a unique representation to them in the form of a "वर्ण".
Now, before I try to explain further please watch these two videos in 6/n & 7/n which shall help in understanding the concept of mantras.
A mantra is a collection of well framed and well versed "शब्द" holding a meaning and consisting of large number of frequencies.
The mantras or shlokas are in Sanskrit and are complex enough to be pronounced clearly. So, if you pronounce them wrongly, the mantra loses its essence as the frequencies will go all wrong.
Scripture says, Narakasura is Asura, who is not a Sura (Angel). The same Scripture says that Narakasura was born to God Maha Vishnu and Goddess Bhudevi (Earth).
@devduttmyth then why wrong precedent today?