Living a life free of guilt and regrets. People make mistakes and can't foresee everything. That's normal. That shouldn't imply any guilt. I was talking specifically about cases where, in advance, you think that you're doing the wrong thing at the cost of short-term convenience.
Regarding KHTML, I don't have any data and can't say for sure. But I'd be surprised if most developers regretted their decision later. They knew in advance that they were getting into an LGPL project that can be used as part of something freedom-restricting. And, in my subjective opinion, Safari isn't so catastrofic and harmful that it defies common expectations of how harmful a freedom-restricting product can be