Why does the alkaline hydrolysis of benzamide yield ammonia?
If the reaction were simply having the form

$\ce{RC(O)NH2 + OH^- &lt;=&gt; RC(O)OH + NH2^-}$

then your reasoning might well apply.  But, in the real world, the carboxylic acid $\ce{RC(O)OH}$ deprotonates (more than the amide $\ce{RC(O)NH2}$) and the proposed, strongly basic amide ion of course protonates to ammonia.  These proton transfer reactions push the displacement forward giving the true reaction

$\ce{RC(O)NH2 + OH^- -&gt; RC(O)O- + NH3}$