It's not the same. In one case you actually buy a stock and hold it because you believe it will go up. You are free to sell if you think it'll go down. On the other side you must borrow a share and sell it with a promise to buy it back in the future. The outcomes and mechanics of them are not equal but opposite, and shorting has many pitfalls, is damaging to the market, damaging to bid/ask, a conflict of interest for institutional lenders, and a number of other issues.