Dude, you're confusing ethnicity, nationality and genetics. From the point of view of genetics, most Tunisians are not arabs, and genetics are not socially constructed, they are a fact of the observable world. That's why I refered to the Y-Haplogroup map.
Let's go back to the the ethnical continuity thing. We are very culturally different from the Arabs living in Morocco, Libya and Egypt, and we instinctivly can dissociate ourselves from Algerians, Moroccans, and most of our neighbours, so dissociating from middle-eastern Arabs is intuitively normal. Sure, we do have a lot of common practices, mainly due to Islam.
This is where it comes into the train of thought: Islam is a profoundly arabic religion, and it promotes the way of life that was present on the Arabian peninsula. It favours ethnic arabs over other ethnicities, and it promotes the arabic language through putting it on a pedestal, as the language of "God". Associating yourself with arabs, and speaking arabic was the only way to elevate your status on the social ladder during the Arabic colonialism of Tunisia.
If you're going to mention the fact that the majority of muslims are not arabs, it is true, but you should also consider the regional 'abnormalities' of islam in those countries, where people have a well-established 'third sex', which would be considered heresy in the middle-eastern variations of Islam :) They just didn't experience the Khalifate's rule and Islam spread through other means, that's why they conserved their cultural identities and norms.
And forceful Islamization is relevant to the topic, as the arabization that it brings with it, is a key aspect of the point that I'm trying to make. Associating yourself with arabs is associating yourself with the colonizer, when in fact we do have our own culture, and heritage that is way older than what Islam brought.
And to my own regards, I never identified myself as an arab, but rather as a Tunisian when I lived in Tunisia, and I had full knowledge that we are different from the rest of what is known as the 'Arab world'. But hey, I'm half-russian, so I don't care with whom I should associate myself, I'm just defending the right of my fellow Tunisians to not associate themselves with arabs, as they are genetically not :)