“Now John answered Him, saying, “Teacher, we saw someone who does not follow us casting out demons in Your name, and we forbade him because he does not follow us.”
“39 But Jesus said, “Do not forbid him, for no one who works a miracle in My name can soon afterward speak evil of Me. 40 For he who is not against us is on our side. 41 For whoever gives you a cup of water to drink in My name, because you belong to Christ, assuredly, I say to you, he will by no means lose his reward.” Mark 9:38-41 (NKJV)
If you’re offended that people are going to a different church than yours; or think they’re only going because of free food or slick marketing, you need to pray for them. And ask yourself if you’re in competition. It could be those people are after the Holy Spirit.