Seek out only sites that don't block adblock, or has no ads. This might include a paid option (for example, youtube premium, or twitch subscription for ad-free viewing).
There are questions substantially more interesting than a reductionist "do I have an innate right to access private websites?"
And of course this situation has different implications if the website offers some sort of an essential service, but that's an entirely different discussion.
Unpleasant might fit better.
It doesn't break ethical rules to ensure ads are shown so income can be generated to pay for hosting.
Many people have agendas, including sometimes very positive agendas, that lead them to support online services of various types in order to further those agendas.
None of this is to say there’s no place for advertising or for paid subscriptions. I’m just saying there are often more options.