Feminism (at least my brand) doesn't oppose sexiness, but it opposes compulsory sexiness.And I'd add that the opposite is also true. It's the difference between dressing modestly because it's comfortable or keeps you warm, and dressing modestly to avoid being jailed or raped because you were "asking for it." Between liking football and Grand Theft Auto because they entertain you, and liking football and Grand Theft Auto because you don't want to dare to have stereotypically "girly" hobbies. Between forgoing makeup because you're too lazy in the morning and forgoing makeup because otherwise you won't be taken seriously at work. Between choosing nerdy t-shirts because you think they're funny, and choosing nerdy t-shirts because your friends will heckle you if you wear anything feminine.
It's the difference between putting on makeup to look like your slutty fantasy, and putting on makeup to leave the house. Between wearing heels because they make your ass tight and your legs long, and wearing heels because they're in your dress code. Between smiling at a sexy stranger and having "hey honey, why aincha smiling" yelled at you. Between having sex because your pussy is wet and your muscles are quivering, and having sex because it's time to put out.
And I'd go further and say it's also the difference between being a sex worker because that's a legitimate career option, and being a sex worker because it's the only way you can eat. It's the difference between sexified female bodies being used as porn, and them being used as decorations and advertisements. Maybe most importantly, it's the difference between women being taken seriously when they talk about sexuality, and women not being taken seriously when they're not sexy enough.
Compulsory anti-sexiness is not the solution to compulsory sexiness. There's not one right way to be a woman.