I'm one of the many cat carers who prefers to keep her cats indoors and in particular at night time since domesticated cats are most vulnerable and in danger at night time, independently from whether they live, in towns and cities or countryside. Cats are not safe outside at night time!
People often believe that it is cruel to keep cats indoors as they need to be free to wonder any time they like. No, that is not true. Cats can learn to live to any environment they find themselves into and the fact that they have adapted to all our living conditions all these years is a good example of this statement. Cats that they were born indoors and lived all their lives indoors they don't miss the life outdoors because they don't know what is to live outdoors and they have adapted to an indoor life. For these cats outside noises and smells are overwhelming and extremely stressful. Just imagine a human that had lived all his life in a city and all of the sudden he/she finds him/herself in the middle of a jungle with all the scary noises and wild life to cope with.
My cats do not feel the urge or the need to go outside when the window or patio door is open and if they accidentally put their head outside to sniff the air they get scared and start growling and hissing at the strange smells and noises and go to hiding till the window or the door has being closed. The same behaviour exhibits my ex-stray cat who doesn't show the slight interest to go outside when the door is open. They are all quite happy living indoors as they get all the attention, food and stimulation they need (our house is a cat friendly environment with more cat toys and furniture that human accessories and furniture).
But my cats do get upset when neighbouring cats are visiting our garden in the middle of the night and in particular when the neighbour's un-neutered tom cat visits the garden and sprays everywhere and even scratches at the door outside and hisses at my cats inside. Which behaviour quite understandable upsets my cats. Of course I could easily just pull the curtains and block the outside view to my cats but that would not be fair to them as they enjoy watching the life outside and in particular all the birds or small mammals that they are frequently visiting.
No, I don't think that blocking their view outside is the best solution. I think the ideal solution would have being if the visiting cat(s) was kept indoors at night for his own good and that his carer took responsibility and have him neutered which could make him less aggressive, not keen on roaming far and not wanting to spray all the time and to mark territory.
When cat carers would finally learn that they need to take responsibility for their cats actions like dog carers? They are responsible for the well being of their cats which means neutering them and keeping them indoors at night time to avoid get them injured and even dying from traffic accidents, other pets and wild animals attacks and even human cruelty. Cats are not wild animals, they are domesticated and as such they need to looked after appropriately by humans, they need to spend more time indoors for their own sake and for the wellbeing of the wild life that is visiting our gardens which includes small birds and other animals.