Apples and oranges.
Terrorists mostly attack soft civilian targets, rather than military, which is cowardly and yes, unacceptable. This is NOT in any way similar to what a sniper does. To equate what terrorists do as a war of attrition is ludicrous, as their methods are to sow the seeds of terror in the general public, not to engage militarily in battle. The current engagement with ISIS/IL is different in these terms, as there is an armed engagement with the belligerents engaging in battle over real estate. One sniper team that can take out key players is an invaluable tool on the battlefield.
A war of attrition is a constant grinding down of your opponent, both in terms of body counts and psychologically, of which a sniper does both.
Your logic is flawed TeeJay.