We could all have the " why should I bother" attitude I am not trying to be a martyr but I work I have more than 1 dc and have outside interests and commitments yet I give up 1 evening a month . Is my time any less valuable than the teachers just because I am a parent?
No, of course your time is not less valuable, but you give 1 evening per month to support the school. Teachers work full time continuously supporting the school, going to weekend events for festivals, special events etc, Parents' evenings, marking work at home, staff meetings, governor meetings, all these can take a chunk of family time. And as other people said, they then have to balance going to their own child's school events!
You should see any help as a bonus, rather than feel resentment because the teachers just can't fit any thing else in. As you say, they did help at the summer fair, how many more events do you expect them to attend?
Schools are not a charity, and PTA fundraising provides extra resources, not vital life saving equipment Put it in to perspective.
Still agree that stealing the sweets is wrong though