When I've spoken to people who think that all religions are basically the same, a little probing reveals that they know practically nothing about any religion in particular. Some will have been raised as Christians, but even they will have only the most cursory understanding of the philosophy.
Marinated in our culture of moral relativism and multiculturalism, they deride any claim that one is better than another. Since they don't know enough to make a judgment call, they assume there isn't enough to be known to make a judgment call and anyone who maintains the superiority of one over another is an ignorant bigot. In fact, it's the open-minded secularist who is ignorant.
It's not just ignorance, either. Sloth plays a big part.
When confronted, for example, by the Islamist who blew away those gays in Orlando, they dismiss it as a one-off and point to Westboro Baptist Church (population: 40) as an example. Even when shown how Islamic republics the world over discriminate against gays, they find excuses and dismiss it. This is done so they don't have to take the time to learn anything.
Wine = Slime
The old saw goes that if you take a spoonful of wine and add it to a glass of gutter slime, you have a glass of gutter slime. If you take a spoonful of gutter slime and add it to a glass if wine, you also have a glass of gutter slime. The secularist concludes that wine=slime and there's no point in learning about either wine or slime. They can safely (and smugly) go on with their lives, "knowing" that all religions are equally slimy.
Judgment Requires Education
When you choose between two functionally similar items on Amazon, you spend time learning enough about them to make a choice. The more complicated the function, the longer it takes to be able to make a good decision. Buying a bottle opener is pretty easy. Choosing a cable modem is harder. Buying a car is much harder still.
Buying a life philosophy is the most difficult of all. All those moving parts, all those complications! There are so many to choose from, too! Some of them come from cultures totally alien to us so learning about them requires more than just learning their basic tenets. What a lot of work.
Jon Stewart Points The Way
Don't do the work. Don't bother learning. Instead, fall back on a dismissive wave of your hand and a sneer at the ignorant bigots who disagree. You can mock them, knowing you are in plentiful, if not good, company. The people we are supposed to respect in politics, the media and academia will provide plenty of cover.
No, you may safely go back to binge-watching Game of Thrones, knowing that you're on the Right Side of History. After all, you're open-minded.