If you buy and legally posess a CD or DVD, it is illegal for you to make copies of that disk to give or sell to someone else.
If you own certain common household products (chemicals) it is illegal to combine them into a form which is explosive.
In England you can not legally watch your TV if you haven't paid the tax.
I am a target shooting enthuiast. I can legally own any type of handgun or long gun but the law strictly regulates the circumstances under which i can use the weapons.
I reload fired cartridges with black powder and smokeless powder that I legally own. I can go to the local hardware store and buy iron pipe without any restrictions. I cannot, however, legally cut a pipe into a 6" length, fill it with gunpowder and screw endcaps on it.
That should be enough examples to disprove your assertion that you can do anything you want with a posession that you legally own. If you need more examples let me know; there are dozens I can come up with.