I can imagine people watching this double episode of the Simpsons thinking 'Wow, wouldn't it be cool if churches were really like that, being so open minded about everything. No sin, all religions are right, whatever feels right for you is good. If you don't believe God is real, that's cool also'
Only trouble is, it makes no sense. If everyone could do what they felt like, there would be anarchy. If morality was subjective then murder, rape, genocide are just a person's moral preferences as much as to love one another and look after those in need are another's moral preference. Sure, there are laws in place that generally stop people doing bad things, but what makes those laws right? On top of that, if you look closely at all religions, they all contradict one another.
The Simpsons is quite dogmatic in their preaching of Universalism. They are preaching that all religions, including atheism are valid. It can be inferred they are saying that if you believe what the Bible says is truth then you are narrow minded.
But they are equally as narrow minded in their wanting you to accept Universalism as truth. Are the Simpsons creators really preaching truth through these episodes?
Where does our conscience come from? Why, deep down, do we know what the right thing is to do? Why do we constantly fight against what we know is right? Is there forgiveness when we know we've gone wrong? Who is it that forgives? How and why can we get forgiveness? Is there life after death?
Science textbooks won't give you these types of answers. Other religious texts attempt to answer some of these questions. You can find answers to all those questions in the one book the Simpsons goes to a lot of trouble to mock and take out of context - The Bible.