Opposing/condemning terrorism does not create terrorism. Justifying and excusing it might, though. What I find curious is how this "OMG, how does what we do create a bad impression of us" mentality seems to flow in only one direction. Don't terrorists and their sympathizers/supporters also contribute to the negative impression some may have of Muslims?
Let me try to explain the post you're responding to so that you might possibly understand it.
First of all, if you read it with some more care, you'll note it holds the caveat "as they claim",
they clearly being IS.
Secondly nothing in said post can possibly be understood as claiming that opposition to terrorism creates the very same.
Thirdly, the insinuation that anyone is excusing terrorism (thus also furthering it in that non-existent stance)) is blatantly absurd.
Lastly, the more people in the West create or support the stance that all Muslims (especially those among us) need be looked upon with grave suspicion to the point that they begin to think we all see them as some kind of lepers, the more resentment this will cause among them. Certainly not with all of them but who even needs there to be a few.
That is the IS game and it's played in the hope and indeed expectation that some of that resentment in some of those Muslims will make for promising recruiting ground.
If you go back to the OP and read alone the part which says
It only took one massive shooting spree for Australia to ban guns, why are they still taking chances with potential Isis sympathizers? you should also realize the implicated broad brush, i.e. Muslims are potential IS sympathizers. Not some Muslims, just Muslims.
Add to that the dishonesty demonstrated by the poster often enough on here, in disingenuously starting threads like these by initially going the "thanks God the worst was foiled" road while actually having a totally different agenda to then push, and that will perhaps address your puzzlement over why threads such as these and coming from where they do,find such criticism.
They're initially a carrion feast then used to pursue a totally different agenda. He's done it often enough in the Europe forum by feasting like some vulture on actual victims (where they occurred), just so as to then go on the usual rant and, should the need occur, to even provide falsified information now and again.
When however something happens like in Hamburg a couple of days ago, where Muslims and others actually prevented a jihadist from fleeing the scene after he'd just knifed a couple of people (one dead) by beating the bastard half senseless with chairs, that thing doesn't show up on his radar. Much as it was on the international news circuit as well.