Arms Arbitrarily Designated as "Assault Weapons" Judicially Restricted

I admit that I am confused by the various interpretations of the Second Amendment.
Massachusetts' ban on assault weapons doesn't violate 2nd Amendment, judge rules | Fox News:

I always thought that it protected the right of the American Individual to possess, carry and use a firearm in defense of  person, property and domicile.

There is no "assault weapon" clause in the Second Amendment; indeed, it has never been defined.

My understanding was that any weapon which might be used by an assailant was equally protected as a legitimate arm to be used by a legitimate private citizen in defense of home, hearth and family.   Further, the "militia" reference in the text suggests that the private citizen ("the militia is ...

Now I am confused by a myriad of laws which limit the rights of a private law-abiding citizen in regard to the type and capacity of the firearm which he/she may use to defend against (for example) a "Home Invader".

If criminals have access to 'prohibited" firearms, why does a private citizen face prison when he/she uses the same weapon as a defense?

What in the Second Amendment defines "Assault Weapons"?

A judge in Massachusetts on Friday ruled against a lawsuit that questioned the state’s ban on assault weapons and large-capacity magazines, declaring that the weapons were not protected by the Second Amendment. Assault weapons are considered to be military firearms, U.S. District Judge William Young said in his ruling, therefore disqualifying them from being included in a citizen’s right to “bear arms.”