ELI5: What is the use of 'condemning' an act (e.g. of terror)?

Short answer: yes. Slightly longer answer: because people are dicks.

Allow me to elaborate. Suppose for a second that there were only two countries in the world: the Yellow country, where people only dress in yellow, and the Purple country, where people only dress in purple. Chances are, the two countries are gonna get along just fine, and there will be embassies, and immigration, and trade, and all that good stuff.

Now suppose that one day a person in Purple country bombs the Yellow embassy. Dozens dead, total bonanza. Objectively, there's no reason to assume that Purple country hired a purple-clad vigilante to exact revenge on their Yellow opponents, but there's no way for Yellow to be sure of this - from their perspective, it's just an attack on their property. So unless Purple leaders denounce the bombing as the whim of a deranged lone wolf, or otherwise not condoned by them, Yellow is just going to assume that they got attacked by Purple.

Now, irl is a lot more complicated, and there are lots of groups one can belong to: nation, religion, ethnicity, etc. So if a terrorist attack, or anything like that, occurs against one group of people, that group is going to assume that their opponents are out to get them. That is, unless leaders from the other group get up and denounce the violence, and extend an olive branch to the victim group.

Hope that helped

/r/explainlikeimfive Thread