What is the argument against the imposition of clerical celibacy as practiced in the Roman Catholic Church? The Roman Catholic Church requires its priests to practice celibacy.  This has not always been the case, though.  In fact, it was not instituted until the 11th century.

Protestant churches have no requirement of celibacy.  So, what is the reason for this? Specifically why do Protestant churches, which began well after the practice had been instituted in the Catholic Church, do not require this of their pastors?
I would like to add a few other Biblical reasons Protestants in general will allow for married Pastors.


  Simon's mother-in-law was in bed with a fever, and they immediately told Jesus about her. -Mark 1:30.


Simon Peter having a mother-in-law necessarily meant that he had a wife. If one of Jesus's own apostles had a wife, then right there is pretty good evidence that pastors today can likewise have wives. 

Here's an argument Paul makes about the matter in 1 Corinthians 9,


  3 This is my defense to those who sit in judgment on me. 4 Don’t we have the right to food and drink? 5 Don’t we have the right to take a believing wife along with us, as do the other apostles and the Lord’s brothers and Cephas[a]? 6 Or is it only I and Barnabas who lack the right to not work for a living?


As we already know that one of the other apostles had a wife, we can safely say that Paul isn't being sarcastic here, but rather stating a very straightforward argument. The apostles were allowed, among other things, money and the right to marry; however, the apostles would at times choose to give up their rights for various reasons, as Paul and Barnabas did with wives, and others did at various points with money among other things (see 1 Cor. 9:12).

Just because some honorably chose to give up those rights, doesn't in any way mean they didn't have those rights in the first place, as Paul states here.

As Protestants don't follow the headship of the Catholic church, they likewise don't observe the things that the Catholic church claims to have "loosed" or "bound," and the scriptural evidence taken without that external input supports a pastor who has the full right to marry if he so chooses.