I would have liked to have been given more time but couldn't have you thinking I conceded the argument so here is a basic case that I would say is on a similar level to the one you constructed:
1. Country has stood the test of time
-Fail. Belgium was invaded during *both* world wars, the first time only 75 years after its birth.
-Fail. Italy was only established in 1861 (practically a bit later), was invaded during *both* world wars, the first time not even 60 years after its birth. Ooo and after the ‘country’ was established some of the nationalists even remarked they needed to now create an Italian identity

2. Country does not have a sizeable important area wanting independence/autonomy
-Fail. The Veneto region has repeatedly demonstrated in a variety of ways a desire for this. Also, sort of connected to this, there is the venetian language many people speak, reaffirming Italy as an amalgamation of different ‘countries’. I’ll just add here the many different dialects of Italian spoken in different regions as well...

3. Country has a strong historic and cultural foundation
-Fail. Italy was long divided into numerous states, with a huge variation in culture, history, traditions and customs reflecting this history of several different states.

4. Country’s inhabitants are not frequently divided by region and see the greater picture of the nation.
-Fail. In a different way to the culture point above, there is frequently noted to be a division between Sardinians, Sicilians, and those of north or central Italy.

5. Country has a clear geographically isolated position.
-Fail. If you look at countries like the UK, Ireland, France, Denmark, Norway, Sweden, Finland, you can clearly see the way the separation between land and seas, mountain ranges etc. naturally define certain areas. Not Belgium. It's simply one of the low countries.
-Fail. Campione d’Italia, I mean talk about failure to be defined... and the land disputes Italy has with France and Austria paint us a picture of a country that has yet to be properly defined, with finishing touches required...

Of course, in my opinion, this should not convince you that Italy is a “non-country”, but I do not see how this argument is significantly weaker than the argument you presented for Belgium, looking at the push for independence/autonomy (which exists to a lesser extent out of the Veneto region as well), and the cultural differences and separation present due to the historically different states present (in this relatively new WESTERN EUROPEAN COUNTRY) as particularly potent.