"All places ... in which ..."
That called a qualifier. Not "ALL PLACES" but rather "All places ... in which ..." See the difference?
:doh "In which the same should be for forts, etc etc".
Not only do they have the power to purchase and regulate the places they purchase from the state legislature, as long as the legislature has given consent, but the congress also has the power to regulate in the same manner US forts in the state, docks, other needed places.... Its essentially saying that congress has the power to regulate forts, dockyards, arsentals in the same matter in which they regulate land they have purchased form the states... Its not saying congress has the power to regulate "all places purchased by the states, but never mind it only applies to docks and arsenals"...
"The constitution of the United States declares that congress shall have power to exercise "exclusive legislation" in all "cases whatsoever" over all places purchased by the consent of the legislature of the state in which the same shall be, for the erection of forts, magazines, arsenals, dockyards and other needful buildings.
When therefore a purchase of land for any of these purposes is made by the national government, and the state legislature has given its consent to the purchase, the land so purchased by the very terms of the constitution ipso facto falls within the exclusive legislation of congress, and the state jurisdiction is completely ousted. This is the necessary result, for exclusive jurisdiction is the attendant upon exclusive legislation; and the consent of the state legislature is by the very terms of the constitution, by which all the states are bound, and to which all are parties, a virtual surrender and cession of its sovereignty over the place. Nor is there anything novel in this construction. It is under the like terms in the same [Volume 3, Page 234] clause of the constitution that exclusive jurisdiction is now exercised by congress in the District of Columbia; for if exclusive jurisdiction and exclusive legislation do not import the same thing, the states could not cede or the United States accept for the purposes enumerated in this clause, any exclusive jurisdiction. And such was manifestly the avowed intention of those wise and great men who framed the constitution."
Article 1, Section 8, Clause 17: United States v. Cornell
You have also ignored this as well: "And also here Hence: Article Four, section 3, clause 2... "The Congress shall have power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States"