If we were so "outraged" about Spanish brutality, why were we willing to tolerate brutal Latin American dictators without any problems when we got rid of the Spanish? Answer: they were scum, but at least they were our scum, to paraphrase a famous American political figure. Your explanation for the Spanish war is simply naive. The US was guided by "providential" self-appointed "destiny" -- to first expand from coast to coast and then to rule sovereign over the hemisphere, and now the world. It's called imperialism, plain and simple. Why sugarcoat it? Let's face it: war was good for America. Wars have in large part contributed to America's power. America sought wars at it does today.
I am not an apologist. I just don't have problems admitting that we are doing what every other Empire did -- go to war on its terms. We waited until 1917 to eneter WWI. In the meantime, we traded and made huge profits with both warring sides. We entered the war when it suited us.
One thing that always came in handy -- to our shame -- was our yellow press. In a democracy, the press has a duty to check on the government (whose job is to serve and not to rule!), to keep it honest, etc. That's why we need a free and independent (critical) press. Unfortunately, our press has often served as the unofficial mouthpiece of the government, using its ability to shape public opinion the way the government wanted it. In the case of "the Maine," the press played a cruicial role in raising the public mood for war, just as FoxNews has done in a fine tradition of "presstitute" reporting.
The yellow press also palyed a part in the raising of the war mood in America in WWI -- helped along with the yellow journalism of our British counterparts. British tabloids were pumping out alleged "massacres" of Belgians, rapes in open squares of Belgian women by Germans, and dead baby stories of Germans impaling little toddlers on Belgian fences. The falcities of such stories became obvious after the fact (always too late), but the important thing is: the war came when we wanted it.
Pearl Harbor did not just happen out of a clear blue. Economic sanctions imposed on Japan were destined to force Japan to either retreat from China or to do something esle to break the sanctions. They chose the latter -- duh! In view of that, one would think that the US would be a little more vigilant about being jumped the way it happend in Pearl Harbor. But, the world was at war, and Hitler was a menace and also a Japanese ally. The US was eager to enter the war to stop the Axis from encroaching on our interests. Until then, we were neutral. But when the time came for a war, we got our war. Mice don't just go to raps, they are coaxed to go to traps. Things do not happen out of a clear blue -- they are usually scripted and choregraphed!
No point in going into the Gulf of Tonkin because there is more than lefty mythology involved. It was a convenient excuse to get Congressional approval.
One must really be naive and believe the rallying calls of politicians who (by definition must) lie. It is totally amazing to me that the words of politicians, the people who rank lowest on the trustworthiness and honesty -- somewhere next to lawyers, are suddenly taken for gospel when it comes to sending American people to die in a far off land with a rallying cry such as a "War to End All Wars."
People don't want to know the truth because they can't handle the truth. We can't just say -- hey, this is what we want because we are the Empire and we set the rules. You don't like it? Sorry, maybe you will call the shots in the next round, but right now this is our show. Why beat around the bush? Because to most a "noble lie" is better than the "naked truth."
If you are looking for lack of credibility, you need to look at the "official truth" and not at those who question it. Critical thinking is always in short supply.