The 30 day rule is biased towards taxing gains: the government is apparently happy to take a piece of my "gains" unconditionally, but will only cut me a break on "losses" under relatively narrow conditions. Don't get stuck with a scenario where you have both gains and losses but the rules force you to pay on the gains without the benefit of offsetting the losses.
It's not biased, it's to prevent a scam called "wash sales," where you constantly realize and accrue tax credits on downtrends, but only pay once on the uptrend.