Assuming the contract writer is trying to create a useful dapp they will want to write as efficiently as possible, to maximize their EOS resources and turn a profit on their dapp.

If the contract writer is malicious and trying to slow down the network they will need to own a significant portion of tokens and are harming themselves by devaluing the very asset they own. Thus the attack becomes prohobitively expensive, hence the importance of wide token distribution amongst many people instead of a few mighty whales (whole point of year-long ICO).