You could say that you disagree with their beliefs and politely explain why. That you use charged words like “blasphemy” and “heresy” indicates to them that you don’t find them worthy of the charity normally afforded to human beings by default, which is what brings on the accusations of anti-Mormonism.
As you see, Nayrb, part of the problem is that a lot of people who would say that they just disagree with Mormons also end up saying that they wouldn’t touch them with a ten-foot-pole. The two don’t have to be linked, but the correlation probably makes a lot of Mormons wary.
You have it exactly.
To ME, 'anti…anything at all" involves
- a willingness to lie about, or misstate, the beliefs of the target religion and think that is just fine as long as the purpose is to defeat that religion, or keep other people from joining it.
- a complete refusal to correct those misstatements or lies when told (by a true believer of the target faith) that they are incorrect.
- Criticism of the target faith that includes insulting language and the use of perjoratives, like, oh…“CULT!” using negative, rather than neutral, language to describe beliefs and practices.
For a terrific example of the sort of thing that is defined as ‘anti,’ go see Jack Chick’s analysis of Catholicism, or look on CARM for just about anything.
There is a very large difference between a ‘critic’ and an ‘anti.’ For instance, posts by Rebecca and most other folks on this list are critical, but do not often fall on the ‘anti-’ side of the line. They will criticize the actual beliefs of the LDS church, (or their interpretation of them, at least) but not descend into ad hominem. Usually.

Their opinions may be strongly worded, but not, generally, over the line of ‘anti.’
Zundrah’s posts, however, exhibit classic “anti-” rhetoric…like "I was surrounded by so many Mormons as you, I think I would die… ’ (this one is very mild, but you can see where the Mormons might look askance at someone who felt that way…) or–oh, go look at post
# 68 on the “Mormons and Catholics Get along fine!” thread.
That one should be framed and used as an example of anti-ism, though one of the weirder and more mild ones. At least no swear words were used.
I guess, if I had to boil my definition of “anti–” down to one word, it would be “liar.” An anti is quite willing to lie–or do anything else s/he thinks is necessary to defeat the enemy (and an anti definitely thinks of the target belief system as ‘the enemy’) even if it is against the rules of the system s/he lives by usually, because of course the ends justify the means.
I think that the cliche’ is 'lying for Jesus."