You technically don't need a license to fish, but without one you'll have to do it in a way they won't know you're doing it. You may also have to do certain unpleasant things to avoid punishment.
The legal team would like you to know that this comment in no way endorses or encourages illegal activity
If adblocking becomes illegal people will still do it (and you should too), some really stupid article tried to claim circumventing Anti-Adblock was illegal under DMCA a while back (interestingly they took it down when people continued to block their ads) and the filter providers did it anyway. Piracy still happens in countries where it's criminalized, ad blocking will continue, though the Quorans (used them as an example because they're the biggest snobs about the law and ethics) and people like them will likely use it less, though it's not like they don't already think it's wrong (some also think it's already illegal).