I would imagine there may be a great difference of opinions on this. Personally I think it is O.K with a few caveats I.e not repeatedly flushing and definitely not intentionally putting them up when it gets anywhere near freezing. A lot of places you would never get to see them without flushing. My record on my local patch is 8 in an area c30 metres squared but have only ever seen one on the deck there. What can be a problem is when they are scarce in an area and they are put up repeatedly. Also have there been many about this winter? I haven't seen any in the usual spot on my local patch this winter.