Drag and drop not working inside Nautilus on Ubuntu 17.10

As Matteo pointed out himself this happens if the Nautilus Flowbox View is enabled. To disable it open a terminal and execute the following:

gsettings set org.gnome.nautilus.preferences use-experimental-views false

Of course you can use the dconf-Editor as well and follow the path above to toggle the setting.

It seems I found the culprit: it's the Nautilus flowbox view! I enabled it because I like the automatic streching, but it seems it's disabling the drag and drop and select option. So for now I disabled it

You can toggle list view mode, and drag'n'drop will work as expected.

Click the button besides the search button, at the top right corner of the window, next to the window controls:

Now you can drag'n'drop.

You can also use Ctrl + mouse wheel to enlarge file/folder thumbnails.