The risk from breast milk is almost impossible to judge. Some children will have been infected in the womb, others will not get infected by breast milk beecher they're already on antivirals.
There are studies where they distinguish between those infected in the womb vs breast milk and don't include women who were taking antiretroviral drugs. Getting an accurate estimate of the risk to infants is hard but there are actually numerous releveant studies so one can get a rough idea but still not an ultra robust one in scientific terms. Nonetheless, it sounds like you think the risk to infants from breast milk is higher than it is. If you want to talk specifics I'm happy to do so and to link relevant studies etc.
Getting an accurate estimate of the risk to adults is even harder (not least because there's no studies for adults) but there are things you can do (and have been done by experts). For example, when comparing the risk to infants vs adults, one needs to factor in things like the fact that infants have immature/underdeveloped immune systems and drink such a high amount of milk per day, in total and just relative to their body size. Other factors include the integrity of their oral mucous membranes, their salivary composition (no/less antibodies and enzymes), the epithelial linings of their GI system and their lower gastric acidity - which all make them more suspectible to HIV compared to adults. There are other biological factors too.
You should also note that, as far as I (and many others) are aware, there are no documented cases of an adult having likely got HIV from breast milk. Obviously though that's not reliable since many patients won't be honest and it's very hard when other risk factors are involved (e.g. unprotected sex, particularly anal) so if they've been present then breast milk would never be the most likely source even if they just had bareback vaginal sex once or twice. Nonethless, don't underestimate the number of adults who do like breast milk, including those who literally drink many litres if the stuff (e.g. those in "adult nursing relationships" and those who buy breast milk online etc) so there should be a lot of potential cases yet none have been identified.
I recommend both looking at the published evidence/studies (yes, they have limitations but whatever you're basing your statements on is clearly much more flawed) and talking to experts who are very well versed about HIV (and yes, I've talked to more than one, including both researchers and doctors) - they'll tell you that the risk is basically just theoretical and they can explain to you why in much more detail than I have. Obviously you should only bother if you're actually interested though.
The closest you can look at in adults is swallowing rather than spitting, which is considerably higher risk.
Absolutely not, they're very different. Semen contains a significantly higher concentration of HIV than breast milk, even if you were to drink lots of breast milk frequently.
Anyway, even though swallowing is higher risk than spitting, the risk is still very low and much lower than the estimated risk of unprotected vaginal sex for example (about 1 in 2,500 - that's only if they actually have HIV of course, which itself is very unlikely).
As long as you don't have gum disease or any cuts, sores, ulcers etc in your mouth and as long as you choose the WG carefully and don't engage in it frequently then the risk really is neglible.
Even if you're the type of person to excessively worry about everything (I'm not saying you are, I'm just speaking generally) you'd have messed up priorities/a warped sense of the relative risks if you'd be worrying so much about HIV from breast milk as opposed to the many other threats to your health and life that are out there.
