Attached is how Emacs displays the usage of underscore out of 
mathematics and friends, for example:

\href{http://www.foo.it/bla_bla.html}{BLA_BLA}

here the underscore is not used to display a subscript as in $A_n$ so 
the result, in my opinion, is wrong. At first sight, it is also almost 
unreadable...

  Angelo