In the bolded sentence, it looks that something is wrong:
Though the purpose of this book as a whole is to look at what could be considered appropriate activity in regard to a cultural site, it is necessary here to look at what might or might not be appropriate commercial activity for the site in question. The particular concerns of religious sites have been referred to already. In general, the ideal is that any commercial activity should be that which is most suitable simultaneously to meet the needs of a site, its presenter and its audience. Mismatches, where activity is inappropriate, spoiling the atmosphere of a place, simply ‘grate’. (Boniface, 1995, p. 100)
Is it grammatical? What does this sentence mean? would you paraphrase it? Shouldn't there be an is before simply?
Boniface, P. (1995). Managing quality cultural tourism: Routledge.