Holding them at bay isn't really good enough. You can be producing twice as much culture as other cdivs are producing tourism and still succumb to ideological pressure.
For example, let's say you go Autocracy, with the goal of rolling the map for a domination victory. Two of the other civs go Freedom and five go Order -- and three of those Order civs are pumping tourism like mad, and are nearly Familiar versus you (30% cumulative tourism vs. your cumulative culture) and on their way to Popular (60%). Let's say they also pass Order as the World Ideology, further pressuring you. If you have neglected tourism, such that you are Unknown to the other civs, then you will find your citizens' unhappiness rising quickly, from Discontent straight to Revolutionary Wave, potentially forcing you to change Ideologies and/or losing cities that flip to other civs. Yes, in this example, Autocracy offers many happiness tenets, which is helpful, but the main purpose of those tenets is to help manage unhappiness from conquests, as you roll the map, and less as defense against ideological pressure.
If, however, you churn out enough tourism to get Exotic and then Familiar on some or all of them, your ideological unhappiness will fall significantly and you can conquer with confidence. (Same goes, of course, for other ideologies and victory conditions.)