The ability to think critically when necessary. To most philosophers and atheists this will sound very strange at first. But the true hidden meaning of most modern religions (as well as philosophies) is this: Fit it to be you. What I have realized is that during the Italian Renaissance and after, religion had to adapt itself to a new world. Where banning something only meant people should do just that. In order to survive, the Christian religion had to change its "battlefield strategy" to insist on love for the Lord and rewarding if you converted instead of fear of being sent to Hell. What this caused without anyone realizing is the most revolutionary thing since the beginning of history. Since religion is more laid back nowadays in civilized countries, it is much more tolerant. For instance, more and more churches allow non-believers to enter their churches and get to know their customs instead of not allowing any "infidels" in. And conversion by force is long gone in the Jewish and Christian religions.
It is because of this tolerance, this belief that people from other religions are equal that I say religions have good mental attributes. That belief of equality in other religions is what created the negative growth of Christianity in the west. When believers hear philosophical ideas and scientific ideas nowadays, they accept it much more easily than one would expect, and sometimes, that even results in conversion. By reacting to the Renaissance with more generous morals, Christianity has doomed itself in the west almost seven hundred years later. It has evolved to be more at peace with science and philosophy, therefore making the jump from Christianity to Atheism much smaller. Now it is possible to talk freely to religious people about advanced philosophy if you phrase it correctly and make sure it doesn't have anything to do with God. By committing to it's survival, Christianity has doomed itself but lasted an extra seven hundred years.
This is why I say that religion has an overall positive effect on humans: it makes them tolerant of others, have decent morals, more children, and nowadays, it gives people a higher tolerance of conversion. It is because of its horrible bans and threats that Christianity has become something that allows people to think freely. As Jesus once said, "there is greater joy in Heaven over one sinner who repents over ninety-nine others who need not repent." This is similar to what Christianity as a religion has done. It was a mess of morals and threats back in medieval times, but now it is a decent religion of free spirits. There is no greater joy on Earth.
Nowadays, you see many religious (non-Buddhist) people delving into philosophy and learning much of it, believing it is irrelevant. That creates a mental system that understands more, is more interested in, and makes others interested as well in philosophy. In the process of doing so, they become much more tolerant, more understanding of others, and much more interested in other religions.
Your Friend, Alejandro Rocha
Note: This article is not intended to encourage any conversion from any religion to atheism or any other religion. This article is not intended to be offensive to religion, atheism, or specifically Christianity in any way. This article praises religions and does not wish to offend or diminish any religion(s).