If a citizen gets in trouble, he expects his government to assist him. Allowing everyone to use his/her judgment is fine if it is understood that you are on your own. The reality is that is never the case.
American travel to Cuba is not going to influence events. The Europeans and Canadians have been going there for a long time. As long as Cuba is a communist dictatorship, it will be very difficult for the people to revolt without outside assistance.
All your points may be valid, but it doesn’t trump the ability to travel freely.
I encourage every American to go to Cuba (as long as they do it legally), to see for themselves the Glory of the Revolution. It speaks for itself.
As it stands now, the US looks like a bully, and it rallies support around Castro. Tens of thousands of Americans on the Malecon in Havana will have a bigger effect than you think.