I understand the sentiment, and I agree that true collective security on international level would be a great thing.
Unfortunately, we don't have an institution yet that can enforce international law. And as long as that is the case, all strong sides will meddle with the sovereignty of weaker countries to some extent. Some do it in ways that might be less sinister and still okay, such as financial aid for political organizations, others are even funding and equipping militias. If the US unilaterally decided not to ever meddle anymore anywhere, these places would immediately fall prey to those others who still do meddle. And the sovereignty of the victims would still not be better protected, the only difference being they're not on the side of the US, but in the hands of some other power.
Another problem with sovereignty, as currently defined by international law, doesn't say anything about the situation inside a country. By international law standards, nobody would be allowed to interveen from the outside, when some genocidal dictator committed a Holocaust, as long as he just did it inside his own borders. Do you think that is okay? Isn't letting it happen even the same as contributing to it, from a moral point of view?