No reason not to treat it just as badly as attempts to mine bitcoin off your CPU. Both of those waste your resources, for someone else's profits, without your consent.
The implied consent is based on trust. The browser is my user agent, it is meant to interpret the data that it gets from HTTP stream the way I want it. I let it do the things as specified in the received data (i.e. by you), because I trust that you're not an asshole and will not abuse that power.
Unfortunately, there are plenty of assholes on-line, who decided to abuse the default behaviour - so now we have ad blockers and reader modes.
Ultimately, it is (by intention and design of the HTTP protocol, and computer networks in general) up to me what I do with the data - if, how, and which parts of it I decide to process.
It is giving consent, in some sense. But make a popular website use visitors' browsers to launch a DDoS attack and you'll find that "anything goes as long as it's the bounds of the sandbox" doesn't really apply.
Apart from that, people can easily take a different view altogether. When I visit a site, I download some bits. Doing so I don't consent to anything -- what I do with these bits is up to me.