I've discovered that a lot of atheists have at least a passing interest in the traditions of Lent. What's up with Lent? Why do Catholics abstain from meat on fridays, but are okay with fish? Isn't fish a meat? Well... yes...
But as an ex-Catholic, all I can say is this: there is nothing inherently objectionable about Lent. It's just a collection of customs and traditions in the forty days* preceding Easter. The forty days represent the time Jesus spent in the desert being tempted by the Devil. Easter, of course, celebrates the most important event of Christianity (as in, should be more important than Christmas), the resurrection.
*Actually, I just found out that it lasts forty-six days, because they don't count the Sundays as part of Lent. I guess I never really bothered to count the days before.
I'm sure there are a lot of Lenten traditions which have disappeared or changed over the ages, but there were a few that even I used to practice. I guess most importantly, there are some special church services. For instance, on Ash Wednesday, the first day of lent, there is a service which ends with everyone with an ash cross smudged on their foreheads. On the fifth sunday, Palm Sunday, we had what I always considered the most exciting service, because instead of being bored as usual, I had a palm leaf to play origami with. Ah... that was a long time ago.
And of course there's the well known tradition of giving up something for lent. I never really bothered with this myself, but I don't consider it any different from the practice of making new years resolutions. If anything, it's more reasonable; many people successfully keep up their sacrifices for forty days, but nobody actually keeps their new years resolution for the entire year.
And then there's the meat. Why doesn't fish count as meat? Because the tradition's motivation has nothing to do with vegetarianism. I imagine the tradition is meant as another form of giving up luxuries. Back then, other meats were more expensive than fish, though nowadays it is reversed (I quite openly prefer tuna sandwiches to turkey sandwiches myself). But honestly, I have no idea. I also have no idea why on Chinese New Year, we receive red packets with money and say "Gung Hey Fat Choi" (it's probably a pun--the Chinese take their puns very seriously). Whatever the motivation was, the current motivation is that it's tradition.
I never really took these traditions very seriously myself. I recognized them for what they were, and assigned them the appropriate priority. It doesn't really matter that much, and no one cares if you skip it. Okay, I guess a few people care. In particular, I bet the Church cares. I think it might have used to be a mortal sin to break some of the dietary restrictions. But that's silly.