Yes! Of course stealing bitcoin is illegal. Still, if you find a forgotten wallet/lost wallet, it'll not be illegal. Because, owner of those bitcoin might have forgot about that.
disagree you are wrong because stealing of bitcoin is illegal in any situation ,so you can not say legal if one person steal bitcoin from other .
Agree with you about this but have one question then what to do with this if some one find any forgotten/lost wallet because he has no contact or any thing about him ?