You are talking semantics. When I mentioned "their airspace" I didn't mean the MATZ - which as you correctly said, is uncontrolled - but the ATZ itself. Put yourself in the ATCO's shoes: he/she sees a plot squawking 7000 and not on his/her frequency approaching the MATZ on a crossing course; who is to say that aircraft is not going to bust the ATZ?
Being in contact with them is also of benefit to
you - that's the idea behind situation awareness. Of course you are entitled not to talk to anyone while crossing a MATZ; whether it's a good idea is another matter. Being in your right will not help a lot when faced with, say, 15 tonnes of Tornado trying to avoid you at 250+ kts
