Fix:
Has the possibility ever occurred to you that in His divine wisdom, when God created man with a free will, not only did He fully know men would not choose the straightest or most direct path to Him, but intended us humans to associate and interact with each other, even while steeped in our various states of sinfulness? And…that this design might allow men to gain insight into their own failings, learn how to overcome them–all the while developing compassion and restraint in criticizing others still struggling.
When invited to a casual social event, we ALWAYS have the option of declining for the most trivial OR substantive reasons. Clearly if you have a specific weakness, good judgment would lead you to avoid events that present you with temptation. However, merely attending an event, which does not have as its purpose the promotion of anything immoral, cannot reasonably or logically be construed to lend a stamp of approval to unrelated (sinful) acts of the hosts. The OP suggested neither that this party was a Roman toga party/orgy, nor an event that otherwise posed a challenge to the OP’s ability to avoid sin–but a holiday party hosted by a homosexual couple. I think THAT is the relevant distinction when deciding whether or not to attend a given function–not the “public” nature of hosts’ sin. The one thing we can safely assume about everyone…no matter how squeaky clean their lifestyle appears to the public…is that they are sinners. The “avoid 'em all” mentality can lead to a pretty sour and solitary existence.