Now, ethically one shouldnt steal from one's friends (or from anyone else for that matter), but in this charming game it is to be encouraged. The problem is, will you get the chance to?!
Well, at worst, you have a 1:50 chance to blow up your friend's progress or something like that. I'm not a pirate who's good at statitistics. Or is it ratios... or percentages... Oh who cares, Im a pirate and I need to steal something from somebody, friend or not!

Sometimes having to spin repeatedly to progress your own island[s] can be a bit tedious (because youre a pirate - who wants to work at anything if youre a pirate?! Defeats the purpose of being one... but I digress.)
Consider this if your tap finger is getting a blister: digging 6 ft deep in the sand to get to your buried treasure isnt fun either, really, and that has to be done sooo... stop whinging and start spinning. You wont get to steal and use up gunpowder unless you buckle down and get to tapping.

Now, if repeatedly blowing up your friends stuff starts to get you down (what kind of a pirate are you?! Shameful...), you can always send them your extra defense shields to relieve those unwanted feelings of remorse. Its not much of a gesture since their island is in flames from your prior seaborn assault, mind you, but you would be surprised how much better it makes you feel about yourself. Its the gesture that counts.
Plus, it will challenge you when you immediately go to blow up their stuff again.

Be a pirate! Its very very wrong, but very very fun. Otherwise pirates wouldnt be one.