The respectable people sure didn't like it that Jesus was willing to associate with people who weren't so respectable. And they said so out loud. And Jesus answered them out loud.
The Parable of the Prodigal Son (or, as some put it, the Parable of the Two Sons, or, as others put it, the Parable of the Waiting Father) is part of his response.
Something like what was upsetting the religious leaders keeps on happening. People who don't behave the way we want our children to grow up should be welcomed into our fellowship? Join our local church? Speak at the Annual Conference? Who makes the rules? Who gets to decide who is following them? Have they read the Bible? Don't they care?
These are questions that the respectable church members can ask. Jesus is talking to the respectable people of his time. But, before we address their attitude, let's look at an example of someone who inarguably does not behave the way he should have.
In the parable, the younger son does behave in an unquestionably poor way. He demands his inheritance before his father dies. He squanders it in dissolute living. Then the economy turns against him. Just as he runs out of money, so does the whole country. He finds an unpleasant job that doesn't even pay well.
So hungry that he's eating pig food, he starts comparing his situation with the one his father provides for his employees.
Whether he would have repented even if his circumstances had been different, we don't know.
What we are told is that even though he no longer feels that he deserves to have the status of a son, he wants to return to his father--because his father treats non-sons well.