Thanks everybody for your comments.
Lucy5, BB and co - I had been doing some research on the internet - but always tend to take it with a pinch of salt, especially for something like this as I know there are lots of people that have extreme views to push on the subject (both for and against) so was hoping to get some MN real life input - which I did and it was great, so thanks again .
Lauriefairiecake - apologies, I didn't mean to cause offence when I put 'social undesirables' - it was late, I was tired, worried and I was trying to keep my post a reasonable length so probably over simplified. You're right, it is a very nice thing to do, to invite somebody home for a meal and a chat if they are having a bad time/ find themselves on the street/ etc. And if it was just that, then that would be fine (so long as they didn't block my driveway ).
However, from some of the research that I had managed to find online, it seems that it can be a lot more than that - inviting people that they have 'picked up' off the street to come and live with them - in order to rehabilitate and recruit them. But initially at least, they don't really know them or if their intentions are to be rehabilitated or to 'freeload' (sorry, am sure there is probably a better way to put this but once again it is late and my only chance to get onto MN and so my brain isn't in top gear). I am also being influenced by past experience - a couple of friends in London previously found that houses near them had been bought and turned into halfway houses (one for ex convicts, one for drug addicts in rehabilitation scheme) after they moved in. Both sets of friends had never had any problems before these houses were set up; afterwards they and their neighbours were burgled several times, there were needles and drug paraphenalia thrown into front gardens, etc etc. To cap it all off, when one of them came to sell (other is still there) the estate agent told them that the price they would get for their property was 5-10% lower than they would have otherwise done, all attributable to the problems the area was having since the rehab scheme had been set up locally. A not insignificant amount that in London had a significant impact on their next property purchase.
So yes, on the one hand I think it is absolutely right to be 'upset and ashamed' at neighbours if you think they have problems when you are basically being nice. On the other hand, with young dc to worry about, if the house next door is suddenly bought by people that I have only had knowledge of being a cult and others having problems (as I said in my OP, this was based on 20-30 years ago and the stuff that I had found on the internet), then it is surely only right to to at least try to find out if there are likely to be any effects or problems or things to be wary of - or not (which is what I am really hoping!) ?
This is one of the reasons I had posted this message to start with - my research online had suggested that this was a potential problem - but as most of the stuff out there tends to be very pro or very anti, it is difficult to know where the actual balance lies and how that will affect my family - who after all are my main concern. I was hoping that I might find out from others who had experienced anything like this if I needed to be be worried or not, if you see what I mean.
And VS - so far have heard no music - hippy, happy clappy or otherwise - from the house, and I they seem pretty straightlaced - the only weed they are likely to have is in the garden after they have been away rather than in a roll up for smoking
And glad to have provided an opportunity for a surreal discussion of christian music!
SB - thanks for the inside info - and you'll have to let me know when you sell your story to the sun as it sounds an interesting read - it's not a paper that I would usually buy (or the daily mail for that matter!)
Thanks again everyone for your comments; sorry this has turned into a long post again, must start trying to get onto mumsnet during the day when I am awake enough to be concise!