Simply because they are practices and beliefs based on faith or an interpretation of Scripture,and not defending is tantamount to being a heretic....The same way the the scientific community defended, as a whole,{few exceptions} the fraudulent work of East Anglica, NOAA and others.
Your comparison still doesn't make sense to me.... First, I don't think all catholics or baptists are required to "defend" any of thier beliefs, in fact, I know they are not. They are under no such obligation. In fact a case may be made that those secure in thier beleifs should not feel a need to defend thier beliefs, beliefs are just that, beleifs and they are based on faith. Science does not rely on faith, and a hypothesis or theory should be reproducable with the same results. For example, if my hypothesis is that water at a certain elevation always boils at 100 degreees C at sea level, it should be possible for anyone to reproduce that result. It's not a beleif, its a fact - water boils at that temp at sea level. See how there is a difference?