personally, the closer a politician is to the office of the Presidency, i think the more they should publically give respect and deference to the President's foreign policy decisions, especially during times of international crisis, because on the House Speaker level, it weakens the image of the President and the United States with their adversaries.
often in the past, visits to foreign governments at odds with the USA have been made by those willing to allow themselves to be used by our enemies for their purposes and to confer the enemy with legitimacy in return for face time and publicity - which could be useful during upcoming elections for instance, or with gaining credibility.
in that sense, the enemy and the traveling dog and pony show become allies against the administration. like Jesse Jackson going to Cuba to buddy up with Fidel or going to Venezuala to pal around with Chavez. or like Louis Farrakan chumming with Arafat in Palestine. Pelosi's trip isn't exactly the same, but the similarities are there.
thats just my opinion. Pelosi is too high ranking to ignore the President, and i find it more than irritating.