Honestly the whole issue could be avoided if ads werent so intrusive and advertisers could be trusted not to shill out malware and trackers with their ads.
I actually saw a video on YouTube (although I forget who uploaded it) wherein the speaker echoed that sentiment, remarking that although they personally didn't mind ads, they understood why people would use adblockers and even said it could be
necessary for safety because of scams and the like - and, thus, they held no sympathy for YouTube because if YouTube had bothered to implement even basic ways of filtering out scam ads and similar things, it wouldn't be in trouble (the speaker held that YouTube is losing what they called a war with adblockers).
Note that all of this is paraphrasing, since I saw it a while ago.
Also: does YouTube claim that adblockers are against its terms of service? If so, they are not
explicitly against its terms of service.
Permissions and Restrictions
You may access and use the Service as made available to you, as long as you comply with this Agreement and applicable law. You may view or listen to Content for your personal, non-commercial use. You may also show YouTube videos through the embeddable YouTube player.
The following restrictions apply to your use of the Service. You are not allowed to:
[subsection 1 not shown]
2. circumvent, disable, fraudulently engage with, or otherwise interfere with any part of the Service (or attempt to do any of these things), including security-related features or features that (a) prevent or restrict the copying or other use of Content or (b) limit the use of the Service or Content;
[subsections 3 through 10 not shown]
Subsection 2 here could potentially be interpreted to mean that adblockers would be
implicitly against the terms of service (by accusing them of interfering with the service itself), but if that's the line they're using, they should really be a lot more clear about it before expecting people to disable adblockers.