Another example, if I give you $50 for something, I can then see where you send that coin. If I recognize the addresses (or can look them up elsewhere) I know exactly what you're buying.
not quite. if you give 'me' $50 for something, you can then see where 'the recipient' sends that coin.
it may be the case that the address i give you for sending the $50, is directly owned by a 3rd party
e.g.
A owes B $50.
C purchases something from A for $50, but A simply gives him B's receiving address.
...also, put me in the
money-laundering-is-not-inherently-bad camp:
Making it a lot easier to launder money...
Tools are neutral. Likewise, as someone said above, free, voluntary exchange should be free.