Alphabet's (GOOG 1.16%) (GOOGL 1.32%) shares are down by 12% this year, partly due to being swept up in broader market volatility. However, the company has faced issues of its own. The stock could remain volatile in the short run, and developments could disrupt the company's dominance in the search engine niche.Despite these challenges, Alphabet remains an excellent stock to buy while its shares are down -- and to hold on to for a while, even with a market capitalization of about $2 trillion. Let me explain ...