Why does 'apt -f install' want to remove all installed packages?

Question

Hiho everyone, I wanted to install the opera browser via their .deb package. I downloaded it from the official site and tried to install it with $ sudo dpkg -i opera-stable_45.0.2552.898_i386.deb but it said I need the apt-transport-https package.

I then tried to install opera using gdebi package installer, successfully.

I guess it somehow messed up my package manager, because executing $ sudo apt -f install now wants to remove all my :amd64 packages ... Here is the output:

Reading package lists...
Building dependency tree...
Reading state information...
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
  apt-transport-https bbswitch-dkms:amd64 evolution-data-server:amd64

[...]

  rtmpdump:amd64 seahorse-daemon:amd64 wmctrl:amd64 xsel:amd64 xserver-xorg-legacy:amd64
  zlib1g-dev:amd64
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  acl alsa-utils anacron aspell at-spi2-core avahi-daemon base-files
  base-passwd bash bc bind9-host binfmt-support binutils

[...]

  yelp zeitgeist-core zenity zip zlib1g-dev
Suggested packages:
  default-mta | mail-transport-agent aspell-doc spellutils avahi-autoipd
  bash-doc binutils-doc

[...]

  cairo-5c xfonts-cyrillic gnome-user-guide zeitgeist-datahub
Recommended packages:
  gir1.2-appindicator3-0.1
The following packages will be REMOVED:
  accountsservice:amd64 acl:amd64 alsa-utils:amd64 anacron:amd64
  apparmor:amd64 apport apport-gtk aptdaemon apturl:amd64

[...]


  yelp:amd64 zeitgeist-core:amd64 zenity:amd64 zip:amd64
The following NEW packages will be installed:
  acl alsa-utils anacron aspell at-spi2-core

[...]

  yelp zeitgeist-core zenity zip zlib1g-dev
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  base-files:amd64 gawk:amd64 (due to base-files:amd64) base-passwd:amd64
  bash:amd64 dash:amd64 (due to bash:amd64)
  debianutils:amd64 (due to bash:amd64) bsdutils:amd64 coreutils:amd64
  dpkg:amd64 (due to dash:amd64) tar:amd64 (due to dpkg:amd64) libc-bin:amd64
  mount:amd64 ncurses-bin:amd64 perl-base:amd64 sed:amd64 util-linux:amd64
0 upgraded, 683 newly installed, 480 to remove and 0 not upgraded.
Need to get 441 MB of archives.
After this operation, 469 MB disk space will be freed.
You are about to do something potentially harmful.
To continue type in the phrase 'Yes, do as I say!'
 ?] 

And the output of apt autoremove:

Reading package lists...
Building dependency tree...
Reading state information...
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 adduser : Depends: perl-base (>= 5.6.0) but it is not installed
           Depends: passwd (>= 1:4.1.5.1-1.1ubuntu6) but it is not installed
 adwaita-icon-theme : Depends: gtk-update-icon-cache but it is not installed
                      Depends: librsvg2-common but it is not installed
 alsa-base : Depends: kmod (>= 17-1) but it is not installed
             Depends: udev but it is not installed
             Recommends: alsa-utils but it is not installed
 apparmor:amd64 : Depends: python3:any

[...]

  xserver-common : Depends: x11-xkb-utils but it is not installed
              Recommends: xauth but it is not installed
yelp:amd64 : Depends: yelp-xsl:amd64 (>= 3.12.0) but it is not installable
zenity:amd64 : Depends: zenity-common:amd64 (= 3.24.0-0ubuntu1) but it is not installable

Now what exactly did I do with installing apt-transport-https and how can I correct this error?