I would ditto what the previous posters said. Our first trip to WDW with DS...7 at the time...was during gayday and it was fine other than crowd size was up as with any large group of tourists in the parks. We are headed back for another trip this year during gayday and I have no concerns other than potential crowds we might encounter. After spending the Sunday before Thanksgiving in the MK, I've learned to just avoid that park completely on a weekend. So, I will this year and every year to come.
If you are interested in the impact that such a large crowd may have, go to the two websites, gayday.com and gaydays.com to check the schedule of events. I did just to see which park might be impacted on the weekend and found the sites to be very interesting and informative.
As for the not to wear red...that color is worn by folks showing support for the gayday gathering. Some folks have gone to the parks wearing red without knowing and have been mortified. Others wear it proudly in support. Point: Make the call for yourself and your family about wearing the color red.
As for public displays of affection...from my experience, minimal. When we took DS I wasn't and am still not a huge fan of groping loved ones in public...doesn't matter from whom. If you have children, maybe be prepared to answer some questions...DS never noticed or if he did he never asked...but I've raised him to be open minded.
Hope you have a great trip! Maybe we'll bump into each other....