Subject: why is ejaculation an involuntary response?

What is the advantage of  ejaculating being an involuntary response? What I 
mean by by involuntary response is that after a certain stimulation the male 
pass the point of no return and cannot stop from ejaculating also a man cannot 
just ejaculate on command, like he does from urination but needs stimulation.

Do all animals have this involuntary response? 

I would think it would make more sense to have ejaculation under complete 
control (like urination) for animals and us as it would be quicker, maybe not 
so good in a certain way ;), but from survival and energy consumption 
standpoint it would.

Thanks for your answer.

Re: why is ejaculation an involuntary response?