Scientists are not sadists, and welfare is taken extremely seriously. What people don't see are the efforts to enrich living environments, provide sedation and analgesia, or the reams of protocols on monitoring and rapidly terminating experiments if the animal is distressed. None of this exists in livestock farming.
Also, for me intelligence is besides the point. If someone is suffering, I don't factor their IQ into whether or not I should help them. What I am saying is that if we are happy to accept animals suffering for our benefit, then we should not be selective about it.
You are making a generalisation here. There is plenty of poor treatment of animals in science. I'm sure things are better than they were but claiming that everything is good and everyone is too doesn't square with human behaviour at all.
The point is that intelligence is sentience. The more aware you are of your own condition the more capable you are of suffering. A jellyfish does not suffer the same as a human, at least not in the way we'd typically measure suffering.
I partially agree with you, but sentience isn't the same as intelligence. From having had dogs I get the impression that most of them are every bit as sentient as I am.
There's also a large amount of speciesism involved in how we feel that's not concerned with intelligence or sentience. As an example, I can conceive of a scenario where someone with a severe learning disability might be less aware and less capable of abstract problem solving than some corvids are. That wouldn't affect my decision of which one to assist in a disaster.
Also, for me intelligence is besides the point. If someone is suffering, I don't factor their IQ into whether or not I should help them. What I am saying is that if we are happy to accept animals suffering for our benefit, then we should not be selective about it.