Why do many religious theists place such a high emphasis on attempting to prove the validity of their religion's authority?

I can’t help but ask this question since this issue has not only been the center of my own life offline, but it appears to be a big issue online as well.

I’m not claiming that all religious people do this, but there appears to be some religions where those followers do this more than the followers of other religions, namely some of the Abrahamic religions. I’m sure there are exceptions to my latter assumption, but there are clear patterns here supporting what I’ve stated thus far.

I figure that most people feel that they’re decent, morally sound individuals who support basic human freedoms, rights and humane treatment of others. So why do many people go out of their way to prove the validity of their particular religious beliefs or their particular god/s while criticizing other people’s religious/spiritual beliefs/nonbeliefs? We even see this when Christian and Muslim apologists (some of whom are respected scientists and other intellectuals) debate against other people with different beliefs from themselves. Some of these people even have their own websites and books supporting their religious agenda.

Do some religious people find their religion’s version of objective morality to be more accurate than that of others version of morality? Could this also be due to culture, pressure to conform, economical/political reasons, fear of divine punishment, etc?

My real question (considering what I’d mentioned above) is this: Why do so many religionists seem obsessed with proving the validity of their religion, even at the expense of attempting to degrade other religions?