Different people have different relationships with Gd. Some see themselves as gds employees and hom hadin being evaluation day. Others are in a romance with Gd and see Rosh Hashanah a time of renewal of the relationship. The former is scary. The latter is exciting!
Source for the latter view? Even if it's an appropriate outlook on Rosh Hashana itself, the whole purpose of selichos is tshuva, and even tshuva mei'ahava requires a more serious approach than song and dance. Every sefer I've ever learned pertaining to elul and the lead-up to the yom hadin speaks of the seriousness of the day and the need for trepidation. There is certainly much to be said about the happiness of the new year, and even the elation that we feel at the end of the day, but I don't see how that pertains to the first night of slichos.
