It is bad advice to simply say, "never take a repayment moratorium" based on anecdotal advice from one very particular set of circumstances.
First of all, many people simply do not have the liquid assets (or any assets) to pay their mortgage while not receiving income. Many Italians who are not able to earn money during this period simply would not have been paying their mortgage regardless of a repayment suspension. So banks may as well get out in front of that rather than waste time sending hundreds of thousands of notices to people who are not able to pay. This is not a choice. Obviously if you can continue to pay your mortgage you should do so.
Second, there is a big difference between temporarily suspending repayment for 2? 3? months and what happened after Katrina where many people had stopped paying for many months or years. There is no way that a few months repayment holiday, even if interest does accrue during that period is going to push many mortgages into negative equity.
Third, Italian mortgages are absolutely capped at 80% LTV and many banks are more comfortable at 60% or even less. This is unheard of by American or UK standards but a consequence is that it would take years of repayment suspension and interest accrual to push into negative equity.
Fourth, negative equity is only relevant if you want to sell. Italians tend not to be super mobile anyway, so even if some people do spend some time in negative equity, only a subset of those people will be "stuck" and prevented from making a move they would otherwise make.