Taking an action based on your belief is not the same as acting in faith, if the thing you are placing your faith into has criteria which do specify the requirements for being a true member of that faith.
The Christian faith sets out the criteria which will indicate if the follower is truly faithful. These criteria are set out in the words and example of Jesus and the nature of God as set out in the bible.
The words and actions of Jesus are easier to recognise because they are obvious and require far less understanding that does the nature of God. For example when Jesus says,
'Love your enemies'
It is hard for me or for any person to interpret that as, 'go and blow up that woman and her child over there'. That is obvious. There are many examples where Jesus demonstrates how we should be operating as followers.
The nature of God explanation is very difficult to explain, but there is a kind of 'knowledge' which can be used to attain the criteria, but as I said it is difficult and I am not sure I can explain very well here but I will try.....
For a while my wife and I had been contemplating how Judas, one of Jesus's original disciples, could spend 3 years in the very presence of God being taught by the greatest person that ever lived in every respect and yet still betray Him and all that had been taught.
How can that happen, to someone in the privileged situation that Judas had found himself in, could I end up the same? These were the questions we posed to ourselves and our pastor.
From what I have read about God and His nature, I have learnt that God is gracious, loving; Ex 34:6
6 Then the Lord passed by in front of him and proclaimed, “The Lord,
the Lord God, compassionate and gracious, slow to anger, and abounding
in lovingkindness and [a]truth;
How can God be compassionate, slow to anger and gracious yet still in the Bible we see many examples where whole cities are wiped out, Jericho, Gomorrah etc?
Well, the fact is God does satisfy all those attributes, but the Bible says He is slow to anger, not without anger. God does give opportunity to individuals and cultures alike, which is why Judas had the greatest opportunity, but Judas also demonstrates human weakness at its very lowest. Judas had the opportunity but he refused it (there are a multitude of theologies about this).
On a cultural level there are examples of God giving opportunity, take Jonah for example, God actually had Jonah swallowed by a sea creature, all because Jonah refused to obey God when he was commanded to preach to the Ninevites, because Jonah knew if he did so the Ninevites would repent. God went to great lengths to provide opportunity for people to turn their hearts back to Him. This message and similar messages serve to point us, mere men, to also afford people the same kindness to give an opportunity to change their heart attitude both in how they treat us and how they treat God.
My point is, when man or entire cultures/nations are confused and have their backs to God, He does not seek to wipe them out, He gives every opportunity, going to the nth degree to give them chance after chance to see the error of their ways. He does not conscript men to kill in His name and even when people knowingly turn their backs on Him, God is still patient until it is their time to answer for their attitude toward Him.
Take this example with the example of Gal 5:22:
19 Now the deeds of the flesh are evident, which are: [i]immorality,
impurity, sensuality, 20 idolatry, sorcery, enmities, strife,
jealousy, outbursts of anger, disputes, dissensions, [j]factions, 21
envying, drunkenness, carousing, and things like these, of which I
forewarn you, just as I have forewarned you, that those who practice
such things will not inherit the kingdom of God.22 But the fruit of
the Spirit is love, joy, peace, patience, kindness, goodness,
faithfulness, 23 gentleness, self-control; against such things there
is no law.
In verse 21, the ones that choose not to accept these opportunities will have their punishment in that they will by no means inherit the kingdom of God. It does not instruct anyone to seek vengeance on God's behalf.
On another note, why would we need to defend God; He is omnipotent enough to do that Himself, but He exercises great patience before doing so, as He did when He gave Noah time to try and persuade people to join Him on the ark, or when Moses persuaded God not to wipe out the Israelites after they escaped from Egypt. God went to massive lengths to give opportunity to people and ultimately gave His own Son.
Moreover, there are specific commands:
31 [a]Treat others the same way you want [b]them to treat you.
What right do we have in passing judgement by our actions:
23 for all [a]have sinned and fall short of the glory of God,
17 For God did not send the Son into the world to judge the world, but
that the world might be saved through Him.
17 ‘You shall not murder.
14 Bless those who persecute [m]you; bless and do not curse. 15
Rejoice with those who rejoice, and weep with those who weep. 16 Be of
the same mind toward one another; do not be haughty in mind, but
[n]associate with the lowly. Do not be wise in your own estimation. 17
Never pay back evil for evil to anyone. [o]Respect what is right in
the sight of all men. 18 If possible, so far as it depends on you, be
at peace with all men. 19 Never take your own revenge, beloved, but
[p]leave room for the wrath of God, for it is written, “Vengeance is
Mine, I will repay,” says the Lord. 20 “But if your enemy is hungry,
feed him, and if he is thirsty, give him a drink; for in so doing you
will heap burning coals on his head.” 21 Do not be overcome by evil,
but overcome evil with good.
"Respect what is right in the sight of ALL men".
Overcome evil with good is the last line I quoted, God gives opportunity, but in the end it is not for us to seek vengeance, for vengeance belongs to God, not man. God promises to repay those who wrong Him, He never asks us to do it for Him.
What makes the difference? One acts purely from their convictions without actually knowing the will of the Father, the other has an understanding of how Jesus would operate in the same situation and chooses to follow the example of Jesus.