Actually straight Christians simply believe what the Bible says about homosexuality and accept God as the moral authority on the subject;
Lev 18:22, 24 - "You shall not lie with a male as with a woman. It is an abomination. Do not defile yourselves with any of these things."
Leviticus 20:13
If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood [shall be] upon them.
Romans 1:26
26 For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:
Romans 1:27
27 And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.
(Romans 1:18-27 - Traces the practice of homosexuality in humanity and defines the practice as the final step in humanity's decline.)
1Cor 6:9-11 - Names homosexuality as one characteristic of the unsaved who are forbidden entrance into the kingdom of God.
1Timothy 1:9-10 - Describes homosexuality as being characteristic of the lawless & the ungodly. We also have destuction of Sodom in which homosexuality is described as "wickedness".
And of course we have the account of God's created intent for sexuality clearly stated in Genesis which is also confirmed by Jesus as the model by which we are to judge all sexual conduct.
Yes, it's exactly that. But for me, my own experience with homosexuals in my life has reinforced (greatly) my faith in God's wisdom on this.