[abhistud]

Refer to the picture given below. So, it says that since in haloarene, carbon is sp2 hybridised, it has more s character and thus better electronegativity. Okay! That sounds fine to me. Now, it says that since it's more electronegative, it holds the electron's a tad bit more. But, isn't that opposing the attraction of electrons towards the chlorine atom thus reducing the polarity and making the bond less stable. I don't UNDERSTAAAND!

[Babcock_Hall]

I think its fine to say that greater s-character leads to shorter, stronger bonds.  The (homolytic) bond dissociation energy for the C-Cl bond in chlorobenzene is greater than it is in chloromethane (400 kJ versus 352, in the table in my textbook).  Speaking only for myself, I am hesitant to bring electronegativity into the discussion.

I would not go so far as to say that bond strength is entirely uncorrelated with chemical reactivity, but I would not explain reactivity in this way, to the exclusion of other factors.  For example, compounds such as chlorobenzene cannot undergo S_N2 substitutions at least partially because the geometry of the transition state cannot be achieved.  This geometrical requirement does not apply to other kinds of substitution reactions.