I have seen many people on many websites posting their BTC/ETH addresses publicly for donations.
Is it absolutely ok and safe to show them? I think so but just wanted to get some opinions from experienced people.
Yes. That's what addresses are for. I personally think that the only reason for hiding your addresses is if you want more privacy. For example, if you do not want your coins to be linked to your identity.
If you want to disclosure an address for donations, there is nothing to worry about.