No guilt here...
I think the bigger sin would be denying your enjoyment of tickling. I love tickling my wife, she understands that it's my "thing". I couldn't imagine having been together all these years and NOT letting her in on it.
I'm a recovering catholic, I was about 18 when I just got sick of everything being my fault (If you're catholic, you can relate ;-) ).
I went through the classic oppressive Irish Catholic education system, and maybe I got my foot fetish from always looking down to avoid eye contact with the sisters of (NO) mercy.
I may have lost my way for a few years, but there's no way you can not believe in a higher power when you see your children born, that's powerful stuff! I do tend to have considerably less belief in institutionalized religion, ESPECIALLY ones that seem hellbent on making you feel bad for every single thing you do.
I will throw this thought out tho, EVERY religion believes in something after death, even ones without a central deity. Why? Because NOBODY can bear to imagine that there is an end. Nobody seems to question the fact that religion likes to preach forgiveness, yet we're all paying STILL for original sin.... or the fact that adam and eve had 2 sons... where'd the rest of us come from? (*cue deliverance banjos*). My faith in organized religion went out the window in school, when this kid who sat two rows from me freaked out and tried to run away, turns out this priest was molesting him, and they were trying to keep it quiet (couldn't silence the press tho, it was ALL over the local news).
The God I believe in was there in the delivery room...twice so far.
As far as tickling and guilt... I'd feel guilty if I never told my wife, and after all these years, went to seek release elsewhere. I'm not ashamed to be a tickler, and I'm not ashamed that it turns me on, in fact, I'm glad I know myself so well.
Which brings up another opressive religious belief... premarital abstenance from sex... I firmly believe that you should find out if you are SEXUALLY compatible before committing the rest of your lives to eachother. We have a wonderful relationship, one that includes tickling... because it's just who I am. I also cater to her needs, the tickling is fun for her, but she's not "aroused" by it.
I try never to consider religion when it comes to tickling... Although, maybe it might be fun to get her in a nun costume for some stocking foot tickling