Obviously they have freedom to waste their breath and good water which would be better utilized on their houseplants. From my reading of your link, it is not just those people whose relatives suggest they be baptized, but to "offer" it to anyone. How you "offer" and at the same time "baptize" that person I'll never know, but it is irrelevant because it isn't going to work.
Still, it is an insult. Mormons have stopped up their ears to the cries of re-traumatization of the families. Trying to force your dead loved ones to convert after they were martyred in the first place adds Insult to injury.
If one Jew said "Gee, that is insulting" they should have the grace to apologize and stop it if they were decent human beings. But they agreed to stop it, and then crawfished, so they also don't honor their agreements. Two strikes for "false" and not "true" church/religion.
That is also one spiritually abusive and therefore 3rd strike "untrue: system to do such a thing. If anything is a big red flag of untruth, forcing conversion would be it. Try baptizing your neighbors' cats in the bathtub -- expect some pushback from their families..
Jews fortunately have a built in fail-safe system against any kind of spiritual hijacking attempts of our souls.
The fail-safe system is Kaddish. We pray for 11 months every time we get together & there are 10 people at least (a minyan) for those 11 months. Then, every year forever after than we remember them (either individuals or groups) on every anniversary of their passing (Yahrzeit).
This remembrance is focused, intense, and substantial. We are still blessing God and remembering martyrs from thousands of years ago on their yearly anniversaries. We still pray for people who lost their lives at Hannukkah when it first happened, the destruction of both temples, as well as the Holocaust.
This is why we see it as so offensive-- Jewish souls are precious and we are all intertwined.
So people in some other religion can set fire to their hair, run around the football field on their knees, -- but it won't work.
I suspect this is some sort of spiritual 'scalp' game of trying to get points to get into heaven at the expense of these Jewish martyrs. I can't help but think such a violation would backfire in the end.