Ops of a channel may kick out a user for any reason they wish, including no reason. They can have any kick message they wish too. Generally, ops will only kick users if they are abusive (and probably deserve the insults if that is the op's wish), but even if the person (in your eyes) doesn't 'deserve' the insult, it is the op's right to do this.
Again, this has nothing to do with mIRC. I have never heard of this "DeCussulator" or whatever you're talking about. Sounds like you could do this through a script anyway, if you really want to block bad text that is. A lot of people don't mind swearing - mIRC should not be edited to be safe for every 11 year old on the Internet.
Try asking in your network's #Help channel and see if they have a mode that filters out swearing, a few do, but it's fairly rare.
The fact is, IRC is not a place of flowers, some nasty stuff happens online - that is the world, that is people. Create your own channel and make your own rules, or go to channels that do not allow swearing (there are many). If you're not prepared to do that, or install a script that might filter out swear words, then, frankly, tough luck.
The point of a kick message is to inform the user of why they are being kicked - it is not the user's right to have the "last word" in any situation. You are free to always /query nickname your-message after you have been kicked however, to say what you think. Depending on what you say, you may end up banned for longer, or ignored.
Regards,
