The U.S. hasn't been perfect, but I'll take it over the alternatives.
And, I'd say protecting democracy for "white countries only" is a simplification. If you're talking about Europe, then we have to consider that the U.S. has also pretty famously fought against European nations and that our subsequent "protection" there was to serve as a bulwark to maintain a world order that benefited the U.S. and democracy.
And, you have to consider that we later "protected" the non-white Japan, Korea, and Vietnam at great cost.
In some of the countries wherein the U.S. could be said to have propped up dictators, there tended to be other geopolitical realities. For instance, many of these were in the Middle East and the U.S. elected to align with the most pliable of the available alternatives. And, in spite of this, the U.S. has also promoted democracy in the region.
You have to also consider the sentiment in many of the countries or regions is/was decidedly anti-American and the choice to support regimes less hostile to U.S. interests is a practical one. Many do not want democracy and the alternative for the U.S. is frequently to topple regimes and attempt to stand up completely new governments (i.e. nation-building). This is an extraordinarily costly endeavor with a high failure rate.
And, all of this in the context of adversarial nations doing the same to promote their own interests.
Again, we're not perfect but the world is a messy place.