I agree that tampering with contraceptives is horrible. I think SimplyMum's point was that if you're with somebody who could do something so callous you need to protect yourself. I'm not sure if I was too OTT but when I didn't have 100% commited relationships it was always condoms plus I had an IUD to protect myself.
I'd have no idea how to prove whether something was tampered with or a genuine accident, I know I barely remember to take my vitamins. I think somebody would be stupid to assume that I'd be able to remember to take a pill at the same time every day.