One of the reasons not to start wars with other countries is it gives them the right to blockade your ports.

But it was closed after a civil war within Gaza where Hamas took over circa 2007, not in response to a war with "other" countries. The blockade has been in places for nearly 20 years.

I think if Israel believes that weapons can be smuggled via sea, which is reasonable given the smuggling via Sinai and Rafah crossing, then they took the rational step of mitigation this risk.

Gazans could smuggle in arms, ergo refugees can't escape out into international waters towards whoever might receive them?

That doesn't make sense, it seems as if they're held hostage by Israel forced to stay in the very land where their own terrorist government might impress them into servitude towards use against Israel.

I can’t image 2 millions gazans going by boats into international waters. To what end? Where would they get so many boats?

The sad part is that Egypt has an obligation under international law to allow refugees into its territory. But Egypt refused.