Honestly what serious raider target's teammembers to heal them?
If someone calls you out for being a bot because you do heal with mouseover, this person is just plain dumb in my opinion. I would rather think one targeting a player is a bot than the other way around because it's so much faster with mouseover.
Think of it that way : targeting players requires one more action or click PER heal , which really adds up in the big picture.
As a shaman? okay maybe not that big of a deal, but take a look at druids, who do you think is faster in rejuvenating all up? the one with mouseover or the one which clicks and then put a reju up?
If you are getting called out for not targeting just tell them you healed as druid back then and learned the valuability of mouseover macros and show them one or two like those :
PHP:
#showtooltip
/cast [nomod, @mouseover][nomod,@player] Purify Spirit
/cast [mod:shift,@mouseover][mod:shift, @player] Unleash Life
PHP:
#showtooltip
/use [nomod,@mouseover,help,nodead][nomod,help,nodead][nomod,@player] Riptide
/use [mod:shift, @mouseover, help][mod:shift, help, nodead][mod:shift, @player]Healing Surge
or tell them you use a grid based heal interface like vuhdo which also allows healing by mouseover.
I myself do not bot as a healer, but heal with mouseover since starting out healing in WotLK.
Imho most people calling out other guys bot, do also bot themself. It's easy to spot if you know what to look for, what you most likely do, if you do it yourself