More properly, we should always support freedom, whether in a democracy, a monarchy or any other form of government. Democracy is just a tool for running a free society and not the only tool to use to do so. There is also a problem with the definition of the word support. Too often our society confuses this word with the words control, dictate and militarily intervene. It is neither right nor practical that we control the entire world.
I agree the United States should always support foreign democracies, and they, in turn, should support us. I think all democratic nations need to be united to show strength and unity at all times so that other nations may see that we stand together. We need to be able to count on these core countries should the need arise.
Support can come in many forms, for this reason I feel it is important for the US to support foreign democracies. This doesn't mean money or assistance needs to change hands. Support could simply mean speaking out about democracy and how it is beneficial. It could mean giving advice or allowing leaders to ask questions or participate in an open forum.
There are many countries in the world today that consider themselves democracies. Sometimes, these democracies are not the best governments. There are many corrupt democracies with leaders that abuse their power for their own benefit. And the United States can't always side with these people. For example, in Iran, the United States supported a democratically elected leader in the country. But soon, the leader started abusing his power and committing many human rights violations, and ultimately, making the country a bad place to live. The only reason the United States supported his government and overlooked these human rights violations is because the leader gave a lot of oil to the United States, and they did not do anything to the leader. This created am uprising in Iran, and the leader of Iran at the time fled to the United States. The people of Iran asked the United States to give him back so he could be punished for his actions, but when the United States refused, the conflict started, and it has been building up ever since.
Just because a country has the magical term Democracy attached to it, does not mean that the US should be responsible for supporting or defending their government. There are many systems of government which function just fine. Democracy, which the US isn't anyways as it is a Republic, is just one of many functional systems. It features flaws just as any government, a notable example in the United States being our first past the post system.