I agree with you, that what's happening in your church is disturbing. A lot of SDA congregations allow other denominations to rent their church buildings for Sunday meetings. I personally see nothing wrong with it.

I would use the opportunities there to sometimes attend their church services and invite them to worship on the Sabbath with us, too. I also see nothing wrong with our pastor speaking for a few minutes to the non-SDA congregations in order to show themselves friendly and invite them to our worship services, and the non-SDA pastor doing the same thing to our congregations. (I know some will disagree with this.)

I think it would be a good thing for a congregation, before renting out the building to another denomination, to have something like training classes for all the members so they would avoid doing and saying things that could be offensive or counterproductive. It might start with Romans 14: 1 as given in the paraphrase, The Message.