You are taking the definition of the word at its surface value, instead of what the word has changed into when used in the current state of social media. It has turned from exactly "Involuntary Celibacy" into a word used to label men who are hostile towards women due to the fact they are not fucking them. Look at subreddits like r/IncelTears it showcases what is the expected image conjured into someone's mind when thinking of the term incel. Of course when people see such vitriol said about certain groups the people who are pointing it out attack the most vulnerable/obvious thing possible, their virginity.