I've often found the "proper" database design is too confusing to users and/or managers. Users will have to understand the complex relationships to enter, inspect, and trouble-shoot data properly. Often they don't. Simplicity often trumps logic and the D.R.Y. Principle even if the limits (simplicity) create extra work in some situations.

Further, you don't know what marketers will dream up in the future and cannot realistically anticipate enough of their harebrained ideas. Try to keep marketing separate from production when possible, but sometimes marketers and/or the bosses want something technically goofy and you have to fudge stuff to get it.

Warn them about possible long-term consequences, but if they insist on Frankenstein, you just have to do it. Get your warnings in writing so that you have a record about their decision when bleep hits the fan later. Further if you avoid complaining a lot in general, then important complaints carry more weight. Otherwise, they'll mistake your important warnings for mundane ones.