The article never made this point.
All it said is that they kill more people. In which case it would seem reasonable to ask, can we save more lives, more effectively with enhanced gun control then with enhanced anti-terrorism measures (I suspect governments are more interested in the later because it really is a power grab for global surveillance and other not-yet-legislated powers).
> a group of people would prefer to dominate their host with violence than to assimilate into the predominant culture.
I think 'dominate' is hardly the right word in this case, even relatively uneducated proponents of the ideology must know that such concept is totally fantastical. Rather it is more likely that assimilation is deemed (by some groups or ideologies) so completely impossible (with as you say the 'predominant culture' and I think this is important part to note, because as westerners we tend to forget that it is indeed predominant and forcefully so) that any form of destruction possible is considered preferable.
> Increasing terrorism is a sign of increasing difficulties assimilating. The ultimate worry is that in 50 years our countries will be split into separate warring tribes.
I really don't think any such worry is realistic, these people are marginalized and completely inconsequential to their nations GDP or the progress of civilization - even North Korea, which would seem the closest in this vein to have some kind of defense against as you put it 'assimilation' I think will ultimately mean very little in terms of global developments.
> I always thought terrorism was feared because it signalled that a group of people would prefer to dominate their host with violence than to assimilate into the predominant culture.
To sum it up, I always thought terrorism was feared because this is an emotion which the government and the media sell.