The number of people not on Twitter, who will not see it unless people decide to give it more publicity and spread the word by reposting the picture will far exceed the few who have seen it and even those may not have noticed the Conservative label at the bottom. I can think of far worse things to say about Nadhim Zahawi than that he acknowledges Good Friday.
If it's a poster plastered all over buses and hoardings I can see why people would find it offensive. Is it something just on a twitter post? I don't do twitter so not really sure how it works. Do you have to purposely log on to someone to see it?