@TheThinker:
Well apart from mass panic reactions being the most probable reaction (although this of course depends a lot of how the aliens would be introduced - if a small craft with a human looking ambassador goes live on TV that would be quite okayish in contrast to an entire alien fleet hovering over a capital broadcasting some "Grey" saying something) you're a bit underestimating things...

For the religious part for example - this isn't all about some cultists comitting suicide. It's about most world religions and so all the Muslims or Christians would suddenly find out that they're not "god's chosen ones" - the one and only unique being with the highest development level of them all. Finding out that there's a race maby million to billion years older than us travelling around with a technology our "official science" can't even really imagine in any realistic or proven way can be quite frightening. People would be totally confused at first: Have they worshipped a wrong god? Will they go to hell for that now? You don't have to be a cultist or something but especially in Europe and America there are immense amount of people really believing in their religion. Their entire "reality" would "go to hell"...

Then there also is going to be this atmosphere of mistrust. It will be pretty much self-evident that all governments around the world pretty much must have lied about this topic. People wouldn't accept their elected representants anymore as they've lied and tricked to an ultimate extent and so pretty much the entire ruling system would break down and martial law probably would get introduced in lots of countries. There also has just to be one bigger country running towards a short-time anarchy to make many more follow if broadcasted news on this topic wouldn't be forbidden in the first place (still the internet would provide the respective informations if it wouldn't get shut down too which on the other hand would create more fear and anger in the first place)...

So you see that just popping up and saying "Hello!" especially if some governments don't want you to do that (which they must certainly don't want because despite any panicking happening or not the trust in them will be gone for sure) is very problematic and as a benevolent race you wouldn't want to do that without any preparations which when you look closer are told to be running for a long time...

Enjoy your meal
Toast