We should not, and will not, enforce a policy of one way or the other. It's impossible. People will provide whatever answer they feel comfortable with, you can vote on which one you think is better. Obviously, if you want more votes you'd want to provide a comprehensive answer and that may include both a Command Line and Graphical way to tackle a problem. ...
In order for an answer to use the GUI, it requires that the answerer knows various things, including:
The Ubuntu flavor the asker uses. ("KDE, Unity or good ol' GNOME?")
What other programs are installed. ("Is Synaptic available?")
Commands largely don't need that. They are in many cases rather universal.
Also: What if the GUI is sluggish, but a short ...
The great thing about Ubuntu is the power of the command line. Sometimes a single command can accomplish a multi-step process in the GUI. To use Ubuntu proficiently and to it's full potential, you have to use the command line.
It's not really a question (more like a community bulletin), but there are two sides to this one. Using the gui is great and should be encouraged for at least one answer on a question.
On the other hand, I REALLY like answers that are simple one-liners as well.
Example of a question with both answers (disclosure, one of them is mine).
We should not be ashamed of the command line and it's often the easiest way of doing something.
The Linux command line is very powerful and while I don't believe we should be giving the impression that real users only use the command line we shouldn't shy away from it either.
In most cases the command line way of doing something will work the same across ...
I usually write answers in two levels:
The general idea of how to solve the problem
A practical way to do #1 either in GUI or command line, usually adjusted to the asker's environment and/or comfort level with command line vs the added complexity of describing steps in GUI (vs copy-paste these incantations).
Users that uses different DE or shell or text ...