Using book.cls makes pdf even pages to be aligned to the right and odd pages to the left

Question

I have started to use book.cls instead of llncs.cls. I have copied the content of book.cls from here.

For some reason, the pdf output has the even pages aligned to the right while the odd pages are (correctly) aligned to the left.

See the following zoomed-out pdf for example:

in this example the first page on the image is an even page so it is aligned to the right. I would like all pages to be aligned as in the second page (which has odd number).

I have the following before \begin{documnet}:

\let\oldvec\vec

\documentclass[ruled,vlined,linesnumbered,commentsnumbered]{book}

\let\vec\oldvec

\usepackage[ruled,vlined,linesnumbered,commentsnumbered]{algorithm2e}
\usepackage{amsmath,amssymb,amsfonts,amsthm}
\usepackage{graphicx}
\usepackage{setspace}
\usepackage{tocloft}
\usepackage{etoolbox}
\patchcmd{\thebibliography}{\chapter*}{\section*}{}{}
\renewcommand{\thesection}{\arabic{section}}
\renewcommand{\cfttoctitlefont}{\large\bfseries}
\setlength{\cftsecindent}{0em}
\setlength\cftaftertoctitleskip{8pt}
\setlength{\cftbeforetoctitleskip}{-3em}
\renewcommand\cftloftitlefont{\large\bfseries}
\setlength{\cftafterloftitleskip}{1\baselineskip}
\setlength{\cftfigindent}{0pt} 

\pagestyle{plain}
\pagenumbering{arabic}
\newcommand {\ignore} [1] {} 
\newtheorem{theorem}{Theorem}
\newtheorem{lemma}{Lemma}
\newtheorem{corollary}{Corollary}
\newtheorem{remark}{Remark}
\newtheorem{definition}{Definition}

What could be the reason and how can I fix this problem ?

Answer 1

As @egreg mentioned in his comment, this is the normal and expected behaviour for a book, as you want the outer margins to be roughly as wide as the two inner margins in sum. This gives a balanced look in duplex print and matches what is considered as good typography.

If you want to disable this behaviour it suffices to provide oneside as a class option:

\documentclass[oneside]{book}

\usepackage{duckuments} % just for dummy content, otherwise not needed

\begin{document}
\duckument % dummy content
\end{document}