Exactly, alot of people complain that "Why cant you let me D: YOU ARE SELFISH" instead of "Ok, he donated and i didnt."
It isnt a punishment for you, its a reward for others.
Damn whiney babies :3
So... what I'm seeing in this discussion is a divide between people with the technical knowledge to get what the problem is here and people that are more concerned with defending the modders and calling names.
If you had read the thread, Sirus, you'd see it's not a question of rewards. If I want a cape all I'd have to do is add another mod, personally- I just edited the minecraft code to use custom capes and skins on my server. If you look at the list of users in the IC2 list you'd see that none(?) of them are for donors. All the names on that list are... in short all this does is add a bunch of IC2 capes to the ForgeCraft server, as someone else said... ePeen.
As far as security... Connecting to a server gives the server admin your IP, Java is an exploitable platform, and the coders are (seriously- no offense... not intended as an insult) amateurs that for the most part are current students of the language. If you are doubtful of a text-file's ability to deliver a payload then you need to do some research on exlpoits before you profess an opinion. Might I suggest starting with how SQL-Injection attacks start?
Finally... time. Death by a thousand paper-cuts. What was the figure mentioned...? That in theory a 10KB file could take up to 2.5s? Which might sound like a lot, but once you factor in network routing and server negotiation that number will likely go up. ...but for the sake of argument- it'll work. So, 2.5s, and if say... 2/3rds of mods start using similar features and figure that by... 60 mods? My count is higher, but it's a nice number.
Lets see... 60 mods, reduced by 1/3rds, multiplied by 2.5 seconds... that alone is over a minute and a half. On top of the initialization FML is already doing. What's the range for 'normal' loadings? 1-3 minutes? Under this scenario even the bottom end of that figure would be doubled. That's for all users. Just to see if 1, 2, 3,..7..9...14..17 people get a special cape. And what happens when different mods start conflicting? Be a pretty stupid way to cause crashes methinks... conflicting capes, and no one wants to drop theirs.
It's all theory and potential worst-case scenario's- but as I stated initially... 'benefits' just a few, 'harms' many. It was a change that could affect overall security and it was just slipped in. Forge has 'update check' hooks built-in ( I believe), if 'cape-check' hooks are needed then take it to Forge. At least that way there is reassurance by being open-source and any potential conflicts, I feel, would be handled better there.
As far as the blacklist functionality... What's the point? Sengir blowing up worlds didn't kill Tekkit, what real difference does text at login have? If you're really against unauthorized mod pack usage and you don't want to get the hate Sengir got then just have it so that IC2 disables itself. ...or forces a client crash with a 'not compatible with xxx modpack' message.
..but even then it would have been phoning home with no notification of the change to users. Bad.
Not to mention that it would qualify as a base-class edit, right? Something modders are typically warned away from 'unless absolutely necessary'?