I think most of his conservative reputation is built on the fact the Left savaged him that one time when he suggested (quite correctly) that homosexual marriage would lead to other deviances being similarly accepted. The Left biliously hates him for that and says he's a "radical, extremist right-wing nut". Hence, we like him.
There was a time when Santorum was a House member and during his first term in the senate when he either was as conservative as I am or he was an excellent actor (take your pick) but I happen to believe he was conservative because he lives his life that way. When reporters or anyone thought they were nailing him, he answered them with truly conservative answers that they used because they believed they could hurt him with his own words, but most normal people thought what he said was appropriate which made him popular because he not only had the right answer, but he wasn't afraid to give it in an "in your face" manner. Sometime after his 2nd term began, he started to be just a little less conservative and since '04 when he campaigned for Specter, he has become truly embarrassing IMO. All I can figure is some fool has sold him on the idea he can be reelected appealing to the same people Specter does (HA!) or he just has the most dreadful instincts of anyone I've ever seen who is in a panic.