I think the issue for the most part is the fact that he was doing all this with an intern in the oval office. Outside the White House, on his own free time maybe it wouldn't have been such a big deal (I say maybe because some people would have probably been just as enthusiastic). But in the oval office, while he was on the job; compare it to your own lives. If you got caught doing it at work and then lied about it, wouldn't you get fired?