To remind you why the Czechs seem so .. paranoid about the USA betraying them. I'll give you a few reasons:
1) 30 September 1938: Munich agreement in violation of French alliance agreements surrenders large portions of Czechoslovakia to Hitler.
2) 15 March 1939: In violation of the Munich agreement, Germany occupies the rest of the country and splits the remnants between Hungary, Poland and a newly 'independent' Slovakia. French and British say nothing.
3) May 5-8 1945: Prague uprising brutally crushed under German tanks while frantic pleas to the American soldiers who were literally on the outskirts of Prague are completely ignored. War ends on May 8th with the Czechs practically begging the Germans not to obliterate what remains of Prague.
4) 1945 Soviet Takeover: Despite being a liberal democracy before World War 2, Britain and the USA agreed to allow the Soviets to occupy Czechoslovakia. Even though the Americans were in large parts of the country first. Agreement was made to obtain support fighting Japan.
5) 1948 Communist Coup: Despite being promised that plural democracy would be ensure the Soviets violate their agreement and install a Communist dictatorship. USA and Britain because of their agreement in 4) can do nothing but accept it.
Following this, despite some efforts (see: Prague Spring), Czechoslovakia remained firmly under occupation by the Soviets.
It doesn't take too much imagination to see where someone might think the Czechs could see parallels between the current situation with respect to missile defence and historical examples. One would think that someone as supposedly smart as Obama would realize this, but I've long accepted that he is not as 'smart' as his proponents give him credit for.