I really don't understand the media hysteria about 100% mortgages.
Negative equity is only a significant problem if you intend to sell while in negative equity.
Ability to repay is far more important.
Example: Person A earns €1,000,000 per year. They buy a house for €500,000, using a 100% mortgage (for whatever reason they use a 100% mortgage instead of paying cash). This mortgage, despite being 100%, is not a problem for them - €500,000 being only 0.5 times their salary. Other example: Person B earns €25,000 per year. They buy a €500,000 house using only a 50% mortgage, due to receiving the other half in an inheritance. Even though this is only a 50% mortgage, it will cripple them as interest rates rise - €250,000 being 10 times their salary.
The percentage is irrelevant in each case - the Person A can easily afford to cover a bit of negative equity if they decide to sell. Person B would need to see prices plummet by over 50% for negative equity to be an issue, and yet person B is in far more dangerous territory than person A.