Big question,

I don't have any facts or pix offhand, but in terms of arranging your presentation, how about incorporating a "myths" versus facts comparison?

For example, in spite of the claim that kids who have gay parents are supposedly messed up, the reality is that these kids are just as "normal" as those in hetero families.

You could also include info on the states that have legalized gay marriage and how life still goes on as before! Similarly, you could also put in info about other nations that have allowed gay marriage.

It's not much, but I hope this helps.