Personally I think the sects are just nutters - but that they may have found a way to "attract" Thargoids - those collected are bound for the dinner plate or worse.
Reminds me of the "Quatermass Conclusion" - https://en.wikipedia.org/wiki/Quatermass_(TV_serial) - where the Cult of Planet People worship at stone circles believing they will be transported to a better life on an alien world. Well worth a watch if you can find it - exactly the classic type of British SF that Elite was born form.
Edit - found the full transcript
Huffity, puffity, Ringstone Round,
If you lose your hat it will never be found,
So pull your britches right up to your chin,
And fasten your cloak with a bright new pin,
And when you are ready, then we can begin,
Huffity, puffity, puff!