A good discussion of this proposed bill can be found here. Mississippi has had a church protection act for several years without problems. I am aware of numerous churches who have taken the initiative to establish a security team and have personally been involved in the formation of several.
From the article (read the whole thing or watch the video):
Alabama law already allows for the use of deadly defensive force under specified circumstances, including:
• when facing an unlawful deadly force threat
• when facing a burglar in a dwelling
• to stop a kidnapping, felony assault, robbery, or forcible rape or sodomy
• to stop a crime involving death, serious physical injury, robbery, kidnapping, sodomy, or sexual assault of a child under 12, while on the premises of a building
All HB 49 does is allow for the use of deadly defensive force under the same circumstances specified in that last bullet point–to stop a crime involving death, serious physical injury, robbery, kidnapping, sodomy, or sexual assault of a child under 12—but to do so on the premises of a church.
By removing that forceful requirement, the Alabama legislature is granting the legal presumption of reasonableness to the defender in highly-defensible property who is facing a “mere” unlawfully present intruder, even if that intruder has not broken anything to gain access to the highly defensible property.