In most states, it isn't illegal for electors to vote differently from the popular vote. In fact, that's one of the justifications for the electoral college in the first place. Electors who don't vote according to their mandate are called "faithless electors," and there are currently rules or laws prohibiting that in some states, and in some states there aren't.
Click on the first link on
this page for a table showing the guidelines for each state. Although even in states where electors are required by law or pledge to vote a certain way, the punishments are relatively minor.
Here's a
list of faithless electors and a description of how the EV system works. Although there have been many cases of faithless electors, it has never changed the outcome of an election.
Personally, I don't like the electoral college system, particularly as it stands now. The electoral college has never served to protect the American government from the decisions of an uninformed populace, which is one of its justifications, and I don't think that its modern justification--states' rights--is all that convincing anymore, either.
But I still don't understand how not voting in a presidential election is an articulate protest against the electoral college. To protest the electoral college, become a faithless elector yourself, write letters to the editor, propose ideas for eliminating it. That gets the message across. Not voting in federal elections doesn't reliably parse as a protest. For any protest to be effective, it has to be clear what you're protesting and why.
Overall, while I don't think not voting makes you a non-citizen or anything, I do think it's the responsibility of a good citizen to research issues and candidates, and to participate in the democratic process by voting, at the very least.
In short, the arguments against voting so far are:
1. My vote doesn't count enough, or the choices aren't close enough to my personal beliefs. This, to me, is all about the compromise. This is a huge, diverse nation, and as such, no single vote is going to sway a national election. Your vote is very unlikely to be a single deciding factor, particularly on the national scale. You are, as you should be, one of a great many. And again, because of the sheer size of the country, compromise is going to play a major role in the choices available to you. The general idea is to narrow down the field of candidates before the general election to two, so that the popular vote is more likely to be a plurality and go to the preferred candidate.
2. The system is broken. Yes, yes, it is. The system is ineffective, it doesn't accurately represent the people, and it needs to be changed. The solution to this is to do something directly, rather than trying to register protest by not voting. Again, it's ineffective and inarticulate. Not voting, if it registers on anyone's radar at all, is more likely to be interpreted as indecision, apathy, or ignorance. You have to make your message clear if you really expect anyone to pay attention to it.
So I don't think that not voting makes you a bad person or undeserving of citizenship. I do not, however, think it's anything to be proud of, and I, like a lot of people, will tend to interpret it as a selfish decision and may even discount non-voters' political opinions to some extent because of it. It still reads as apathy to me, and those who are apathetic and uninterested in the subject they're discussing tend not to have informed opinions. In other words, if you don't care enough about the subject to take a few minutes out of your day to vote once a year, or even once every four years, it strikes me that you just don't take it all that seriously.