What makes you think that he is a conservative?
I've seen no evidence whatsoever. Anything that he may have done correctly was likely borne of political expediency, not conviction.
He thinks that there is a government solution to everything including speaking badly of the government. That alone should disqualify him.
You see no evidence? Well here is some evidence even though I'm not sure it justifies voting for McCain for President.
McCain on Taxes is more of a "moderate" but he has supported far more tax cuts.
He has provided unwavering support for the Iraq War.
He is generally Pro-Life. http://www.issues2000.org/Senate/John_McCain_Abortion.htm
McCain supported the ban in Arizona on Gay Marriage but retreated when confronted with the attempt at moving forward a constitutional amendment but he is clearly not a pro homosexual agenda Republican.
http://www.azcentral.com/arizonarepublic/news/articles/0826initiatives26.html
http://www.cnn.com/2004/ALLPOLITICS/07/14/samesex.marriage/
He even came out in support of teaching intelligent design which of course is pretty much a conservative stance even though there are atheists who support ID.
http://www.dailykos.com/story/2005/10/31/165942/40
http://abcnews.go.com/US/wireStory?id=315976
Now I'm not saying I'd vote for McCain in a primary but if it were a choice between him and some real liberal I'd do it. McCain wants to be a populist, he could be a great President if he could just resist throwing bones to liberal dogs yapping at him but I doubt that will change.