Joel Thomas, one of my commenters, makes a good point. The War on Terror will make us safer in the long run, but in the short run it might make life more dangerous. Even if our safety level does not increase monotonically we'll be better off in the long-run for having defeated terror than we would have been if we had endured the status quo ante forever.
This argument undermines the the second half of the combined claim that (a) attacking Iraq incited more world terrorism and (b) that such incitement is bad and demonstrates that we shouldn't have attacked Iraq. (a) may be true, but even if it is it doesn't necessarily follow that (b) is true. The goal of the War on Terror is to reduce the long-term threat level, even if we have to make intermediate sacrifices towards that end.
Since there's no real way to know what the long-term effects of the status quo ante would have been, it's impossible to prove or disprove (b). (b) becomes intangible, even if (a) can be numerically demonstrated.