True enough although by the same argument if they have shitcoins no one is really going to bother checking where the coins are moving while with Bitcoin it is easier to figure out because of all the attention on it when large amount start moving.
You can only use Bitcoins to move large amounts. You cannot use shitcoins to move large amounts. That is because the shitcoin market cap is too small to move large amounts.
Anyway, you will have to convert them in to Bitcoin before you cashes out.
True but when you convert them to Bitcoin from Shitcoins the trail becomes a lot more complicated than if it was just Bitcoins by themselves since to my knowledge their is no blockexplorer to follow on most of them.
Example
Buy 100,000 Sexcoins using tainted BTC on an exchange
Move Sexcoins somewhere else
Then buy Another Coin like NMC on a second exchange
Move to the third exchange and convert back to BTC
Then cash out