In the article posted above, just replace Esther with David's encounter with Bathsheba and you would get the same, albeit flawed rhetorical point. From the article cited:
"What child of God would ever enter a beauty contest in the first place? What child of God would ever enter a beauty contest, thereby agreeing to fornication with the one sponsoring it? It was a gross violation of the seventh commandment... By agreeing to marry Ahasuerus, Esther violated the marriage ordinance God had established in paradise, for she contradicted the purpose of marriage by being unequally yoked to an unbeliever."
Let's apply this thinking to David: What child of God would watch a woman bathing with lust? What child of God would commit fornication with her? King David had the added sin that he was her superior and was commanded to bless her and protect her as per the Fifth Commandment. What child of God would murder Bathsheba's husband - a violation of the 6th Commandment.
David too violated the marriage ordinance God had established in paradise by taking multiple wives. I must not be tracking the logic used against Esther in the article.
As others have noted - it is improper for us to expect perfection from any of God's saints. As Logan noted: I think some charity towards Esther is warranted. Imagine the pressure being brought to bear on her by King Xerxes! While I agree that she should not have fornicated with him, she is a fallen person. It is a mark of God's longsuffering that while we are faithless He remains faithful.
It is interesting to note that in the midst of Esther's famous statement, "if I perish, I perish" there is something else mentioned:
Chapter 4:15 Then Esther told them to reply to Mordecai: 16 “Go, gather all the Jews who are present in Shushan, and fast for me; neither eat nor drink for three days, night or day. My maids and I will fast likewise. And so I will go to the king, which is against the law; and if I perish, I perish!”
It is interesting that Esther also has her maids join her in her fasting, which is a religious duty and as their superior she also commands them to fast.
Personal thoughts: I have had those moments where my faith has flickered, had wavered, and had been so dim as to almost be undetectable. However, God has kindled my faith so that in the end I was proven to be faithful even after turning away from God's commands. Usually after a good kick in the pants
When I read Esther I detect something similar, especially for the low condition that the Church found itself in in her day: I certainly do not think it is unexpected that she participates in the harem in the face of the terrible man that was King Xerxes.
But almost all persons of faith in the Bible and in life come from vile and wicked conditions that the grace of God brings them out of. As mentioned King David is another example of this. A man who commits many deeds of wickedness. David needed a Savior who would never break God's Law. So did Esther. So do I.
I was blessed recently to listen to a series of sermons on Esther by the Rev. Kenneth Stewart. I love Rev. Stewart's preaching in general, but this series was one of his best:
http://www.sermonaudio.com/sermoninfo.asp?SID=33151448190