The mall is a private business, and should have the constitutional right to decide who is allowed to be in the mall, and what they can do.
It’s like a “no solicitation” rule. Surely the mall has a right not to allow people to come into a store and beg people for money, just like you have a right to tell people to leave your front porch if they try to convert you to their religion.
This rule was too intrusive. It attempted to control the conversation between consenting participants. In this instance, the person suing was a youth pastor who was sharing his faith with three young people who willingly engaged in conversation with him. The mall asked him to leave and had him arrested because of the content of his private speech. That is unconstitutional.
If he had gotten up on a bench and started to preach, disrupting the normal operation of the mall and interfering with commerce, they could have stopped him. If he was attempting to sell Bibles or religious items without permission, they could have stopped him. But to have him arrested for engaging in a private conversation with willing participants just because the conversation was religious in nature goes too far.
Your analogy of someone on your front porch is off base as well. As a general rule, you do not spend millions in advertising asking people to come visit your front porch. A mall does, and in doing so becomes a quasi-public forum or “public accommodation”. This places some limits on their ability to infringe on the rights of their customers.