Perhaps we should start dispelling myths. Perhaps all those who identify as feminists - whether 'fun-fem' or radical, FWR hater or lover - should start stating how they feel about joy and sex. 
I'll start.
I am a feminist.
I laugh at least once every day and am probably the happiest person I know TBH. In RL I am known for positivity and while I'm not going to be auditioning for a position at Butlins in a redcoat, I think I have a healthily developed sense of fun.
That doesn't stop me getting angry about inequality and fighting to do something about it. Does everyone who has a cause have to be brooding? If so, I'll get my coat. But if they are brooding, so what? If you feel passionate about a cause and you suffer a set-back/unjustified criticism, it's only human to get pissed off about it and bite back from time to time. Anger can be a positive force for change.
I like sex. Don't want to stray into TMI territory but I'm quite adventurous and open-minded about it. As long as it doesn't involve children or animals, and consent is unequivocal, anything goes in my book. I just think the question of what is consent needs a closer examination. What's wrong with that? Why is that threatening and considered disliking of sex?
I like men, but I don't like fuckwits. I don't think all men are fuckwits, but I do think quite a few are - not most, but quite a few. Unfortunately, because we live in a male-dominated society, the effect these few have on what is perceived as normal is disproportionate and does a lot of women a lot of harm. The normalisation of rape myths (she was asking for it) and domestic violence excuses (she provoked him) are but two extreme examples. There are also subtle ones that are far more insidious. I like to examine those and pull them apart so that other women don't have to fall foul of them in the future.
What is joyless or disliking of sex in all that? I am a great believer in the old Abraham Lincoln quote that "most people are about as happy as they make up their minds to be." But I'm not a passive doormat either. The ability to find happiness in what you have is a great coping philosophy for daily life, but it doesn't exactly encourage change and progression does it, and it's quite often used to keep people in their place.
I think it's possible to be happy, joyful, sexual and still be a feminist.
I don't know many feminists who disagree with that actually - it tends to be those who don't really understand what feminism is or feel threatened by it who come up with the stereotype that feminists hate life in general, men in particular, and any form of sex full stop.