Why do you lock up your houses?

[Claire_Pendragon]

Yeah since clearly it is wrong to simply not want people walking around in your house.

Noticed how you jumped to conclusions?
It's because people tend to not understand others, which is the whole point of this thread.
The OP understands that people dont want others in their house.
What the OP does NOT understand, is WHY.

You can say "Just because" but that still doesnt actually answer it.

If you don't know, thats fine, but it is kind of pointless to answer the OPs question that way.